Comparing the factorial structure, invariance, and predictive validity of transtheoretical model constructs for alcohol use across restricted and unrestricted settings

With substance abuse treatment expanding in prisons and jails, understanding how behavior change interacts with a restricted setting becomes more essential. The Transtheoretical Model (TTM) has been used to understand intentional behavior change in unrestricted settings, however, evidence indicates restrictive settings can affect the measurement and structure of the TTM constructs. The present study examined data from problem drinkers at baseline and end-of-treatment from three studies: (1) Project CARE (n = 187) recruited inmates from a large county jail; (2) Project Check-In (n = 116) recruited inmates from a state prison; (3) Project MATCH, a large multi-site alcohol study had two recruitment arms, aftercare (n = 724 pre-treatment and 650 post-treatment) and outpatient (n = 912 pre-treatment and 844 post-treatment). The analyses were conducted using cross-sectional data to test for non-invariance of measures of the TTM constructs: readiness, confidence, temptation, and processes of change (Structural Equation Modeling, SEM) across restricted and unrestricted settings. Two restricted (jail and aftercare) and one unrestricted group (outpatient) entering treatment and one restricted (prison) and two unrestricted groups (aftercare and outpatient) at end-of-treatment were contrasted. In addition TTM end-of-treatment profiles were tested as predictors of 12 month drinking outcomes (Profile Analysis). Although SEM did not indicate structural differences in the overall TTM construct model across setting types, there were factor structure differences on the confidence and temptation constructs at pre-treatment and in the factor structure of the behavioral processes at the end-of-treatment. For pre-treatment temptation and confidence, differences were found in the social situations factor loadings and in the variance for the confidence and temptation latent factors. For the end-of-treatment behavioral processes, differences across the restricted and unrestricted settings were identified in the counter-conditioning and stimulus control factor loadings. The TTM end-of-treatment profiles were not predictive of drinking outcomes in the prison sample. Both pre and post-treatment differences in structure across setting types involved constructs operationalized with behaviors that are limited for those in restricted settings. These studies suggest the TTM is a viable model for explicating addictive behavior change in restricted settings but calls for modification of subscale items that refer to specific behaviors and caution in interpreting the mean differences across setting types for problem drinkers. ^

Self-reported participation and perceived barriers to exercise in South Texas Hispanic adults

National data show that Hispanics report low levels of physical activity. Limited information on barriers to exercise in this population exists in the literature. Surveys were administered to 398 Hispanic participants from two colonias in South Texas to investigate self-reported levels of and perceived barriers to exercise. Results show that 67.6% of respondents did not meet physical activity recommendations of at least 150 minutes per week, as compared to 55.6% nationally. Overall, the most frequently reported barriers included “lack of time”, “very tired” and “lack of self-discipline” to exercise. An exploratory factor analysis of the barriers reported by participants not meeting physical activity recommendations resulted in a three-factor structure. A unidimensional scale was found for participants meeting recommendations. Findings suggest that future interventions should be specific to gender and exercise level to address the high prevalence of inactivity in this population. ^

An epidemiologic evaluation of a worksite based intervention

The healthcare industry spends billions on worker injury and employee turnover. Hospitals and healthcare settings have one of the highest rates of lost days due to injuries. The occupational hazards for healthcare workers can be classified into biological, chemical, ergonomic, physical, organizational, and psychosocial. Therefore, interventions addressing a range of occupational health risks are needed to prevent injuries and reduce turnover and reduce costs. ^ The Sacred Vocation Program (SVP) seeks to change the content of work, i.e., the meaningfulness of work, to improve work environments. The SVP intervenes at both the individual and organizational level. First the SVP attempts to connect healthcare workers with meaning from their work through a series of 5 self-discovery group sessions. In a sixth session the graduates take an oath recommitting them to do their work as a vocation. Once motivated to connect with meaning in their work, a representative employee group meets in a second set of five meetings. This representative group suggests organizational changes to create a culture that supports employees in their calling. The employees present their plan in the twelfth session to management beginning a new phase in the existing dialogue between employees and management. ^ The SVP was implemented in a large Dallas hospital (almost 1000 licensed beds). The Baylor University Medical Center (BUMC) Pastoral Care department invited front-line caregivers (primarily Patient Care Assistants, PCAs, or Patient Care Technicians, PCTs) to participate in the SVP. Participants completed SVP questionnaires at the beginning and following SVP implementation. Following implementation, employer records were collected on injury, absence and turnover to further evaluate the program's effectiveness on metrics that are meaningful to managers in assessing organizational performance. This provided an opportunity to perform an epidemiological evaluation of the intervention using the two sources of information: employee self-reports and employer administrative data. ^ The ability to evaluate the effectiveness of the SVP on program outcomes could be limited by the strength of the measures used. An ordinal CFA performed on baseline SVP questionnaire measurements examined the construct validity and reliability of the SVP scales. Scales whose item-factor structure was confirmed in ordinal CFA were evaluated for their psychometric properties (i.e., reliability, mean, ceiling and floor effects). CFA supported the construct validity of six of the proposed scales: blocks to spirituality, meaning at work, work satisfaction, affective commitment, collaborative communication, and MHI-5. Five of the six scales confirmed had acceptable measures of reliability (all but MHI-5 had α>0.7). All six scales had a high percentage (>30%) of the scores at the ceiling. These findings supported the use of these items in the evaluation of change although strong ceiling effects may hinder discerning change. ^ Next, the confirmed SVP scales were used to evaluate whether the intervention improved program constructs. To evaluate the SVP a one group pretest-posttest design compared participants’ self-reports before and after the intervention. It was hypothesized that measurements of reduced blocks to spirituality (α = 0.76), meaning at work (α = 0.86), collaborative communication (α = 0.67) and SVP job tasks (α = 0.97) would improve following SVP implementation. The SVP job tasks scale was included even though it was not included in the ordinal CFA analysis due to a limited sample and high inter-item correlation. Changes in scaled measurements were assessed using multilevel linear regression methods. All post-intervention measurements increased (increases <0.28 points) but only reduced blocks to spirituality was statistically significant (0.22 points on a scale from 1 to 7, p < 0.05) after adjustment for covariates. Intensity of the intervention (stratifying on high participation units) strengthened effects; but were not statistically significant. The findings provide preliminary support for the hypothesis that meaning in work can be improved and, importantly, lend greater credence to any observed improvements in the outcomes. (Abstract shortened by UMI.)^

Understanding treatment-related symptoms, symptom management techniques, and symptom management self-efficacy in a sample of non-muscle invasive bladder cancer patients

The current literature available on bladder cancer symptom management from the perspective of the patients themselves is limited. There is also limited psychosocial research specific to bladder cancer patients and no previous studies have developed and validated measures for bladder cancer patients’ symptom management self-efficacy. The purpose of this study was to investigate non-muscle invasive bladder cancer patients’ health related quality of life through two main study objectives: (1) to describe the treatment related symptoms, reported effectiveness of symptom-management techniques, and the advice a sample of non-muscle invasive bladder cancer patients would convey to physicians and future patients; and (2) to evaluate Lepore’s symptom management self-efficacy measure on a sample of non-muscle invasive bladder cancer patients. Methods. A total of twelve (n=12) non-muscle invasive bladder cancer patients participated in an in-depth interview and a sample of 46 (n=4) non-muscle invasive bladder cancer patients participated in the symptom-management self-efficacy survey. Results. A total of five symptom categories emerged for the participants’ 59 reported symptoms. Four symptom management categories emerged out of the 71 reported techniques. A total of 62% of the participants’ treatment related symptom-management techniques were reported as effective in managing their treatment-related symptoms. Five advice categories emerged out of the in-depth interviews: service delivery; medical advice; physician-patient communication; encouragement; and no advice. An exploratory factor analysis indicated a single-factor structure for the total population and a multiple factor structure for three subgroups: all males, married males, and all married participants. Conclusion. These findings can inform physicians and patients of effective symptom-management techniques thus improving patients’ health-related quality of life. The advice these patients’ impart can improve service-delivery and patient education.^

An examination of the cross-cultural reliability and construct validity of a measure of loneliness

Loneliness is a pervasive, rather common experience in American culture, particularly notable among adolescents. However, the phenomenon is not well documented in the cross-cultural psychiatric literature. For psychiatric epidemiology to encompass a wide array of psychopathologic phenomena, it is important to develop useful measures to characterize and classify both non-clinical and clinical dysfunction in diverse subgroups and cultures.^ The goal of this research was to examine the cross-cultural reliability and construct validity of a scale designed to measure loneliness. The Roberts Loneliness Scale (RLS-8) was administered to 4,060 adolescents ages 10-19 years enrolled in high schools along either side of the Texas-Tamaulipas border region between the U.S. and Mexico. Data collected in 1988 from a study focusing on substance use and psychological distress among adolescents in these regions were used to examine the operating characteristics of the RLS-8. A sample stratified by nationality and language, age, gender, and grade was used for analysis.^ Results indicated that in general the RLS-8 has moderate reliability in the U.S. sample, but not in the Mexican sample. Validity analyses demonstrated that there was evidence for convergent validity of the RLS-8 in the U.S. sample, but none in the Mexican sample. Discriminant validity of the measures in neither sample could be established. Based on the factor structure of the RLS-8, two subscales were created and analyzed for construct validity. Evidence for convergent validity was established for both subscales in both national samples. However, the discriminant validity of the measure remains unsubstantiated in both national samples. Also, the dimensionality of the scale is unresolved.^ One primary goal for future cross-cultural research would be to develop and test better defined culture-specific models of loneliness within the two cultures. From such scientific endeavor, measures of loneliness can be developed or reconstructed to classify the phenomenon in the same manner across cultures. Since estimates of prevalence and incidence are contingent upon reliable and valid screening or diagnostic measures, this objective would serve as an important foundation for future psychiatric epidemiologic inquiry into loneliness. ^

Parental influence on adolescent smoking initiation among Mexican origin youth

Smoking is often initiated in adolescence through trying or experimenting with cigarettes. Smoking initiation is the beginning critical stage in the smoking trajectory often resulting in addiction. This dissertation examined the effect of parenting variables on smoking initiation behavior among 11–14 year old Mexican origin adolescents, a largely understudied group. The participants in this study were part of a population-based cohort of Mexican origin adolescents residing in Houston, Texas. ^ Aim 1 of this study assessed the appropriateness of the Family Life Questionnaire (FLQ) among Mexican origin adolescents. Second order confirmatory factor analysis (CFA) was performed to examine the factor structure of the FLQ and measurement invariance testing was conducted to evaluate the cross-cultural validity of this scale. Aim 2 analyzed cross-sectional associations between parenting variables and adolescent ever tried smoking behavior while aim 3 focused on prospective examination of changes in parenting variables from baseline to final follow-up on ever tried smoking behavior among never smokers. ^ Overall, the results of the CFA indicated that the original factor structure of the FLQ, with alterations, was a good fit for the Mexican origin adolescents. The measurement invariance analysis of the modified FLQ scale indicated adequate measurement invariance. The aim 2 cross-sectional analyses indicated that family cohesion was significantly associated with lower odds of ever tried smoking. Authoritarian parenting was significantly associated with smoking initiation only at the baseline while family conflict was significantly associated with smoking initiation only at the two-year final home visit. The findings from the aim 3 prospective analysis indicated that changes in levels of family cohesion and conflict are important predictors of smoking initiation among those who have never tried smoking. Specifically, perceiving low levels of family cohesion and a decrease in the family cohesion over two years, as well as perceiving high levels of family conflict and an increase in conflict over two years was associated with smoking initiation among never smokers. ^ In general, the findings of this study provide important insights on the links between parenting and adolescent smoking and assist in designing prevention and intervention programs that emphasize the role of family bonding to prevent adolescent smoking behavior. Family education programs for Mexican culture could also highlight the positive effects of authoritarian practices and good family communication to prevent family conflict and subsequent smoking behavior.^

Insights into transcription enhancer factor 1 (TEF-1) activity from the solution structure of the TEA domain.

Transcription enhancer factor 1 is essential for cardiac, skeletal, and smooth muscle development and uses its N-terminal TEA domain (TEAD) to bind M-CAT elements. Here, we present the first structure of TEAD and show that it is a three-helix bundle with a homeodomain fold. Structural data reveal how TEAD binds DNA. Using structure-function correlations, we find that the L1 loop is essential for cooperative loading of TEAD molecules on to tandemly duplicated M-CAT sites. Furthermore, using a microarray chip-based assay, we establish that known binding sites of the full-length protein are only a subset of DNA elements recognized by TEAD. Our results provide a model for understanding the regulation of genome-wide gene expression during development by TEA/ATTS family of transcription factors.

Regulation of chromatin structure, Smad binding and AFP expression by the Forkhead box transcription factor: Foxa1

Transcription factors must be able to access their DNA binding sites to either activate or repress transcription. However, DNA wrapping and compaction into chromatin occludes most binding sites from ready access by proteins. Pioneer transcription factors are capable of binding their DNA elements within a condensed chromatin context and then reducing the level of nucleosome occupancy so that the chromatin structure is more accessible. This altered accessibility increases the probability of other transcription factors binding to their own DNA binding elements. My hypothesis is that Foxa1, a ‘pioneer’ transcription factor, activates alpha-fetoprotein (AFP) expression by binding DNA in a chromatinized environment, reducing the nucleosome occupancy and facilitating binding of additional transcription factors.^ Using retinoic-acid differentiated mouse embryonic stem cells, we illustrate a mechanism for activation of the tumor marker AFP by the pioneer transcription factor Foxa1 and TGF-β downstream effector transcription factors Smad2 and Smad4. In differentiating embryonic stem cells, binding of the Foxa1 forkhead box transcription factor to chromatin reduces nucleosome occupancy and levels of linker histone H1 at the AFP distal promoter. The more accessible DNA is subsequently bound by the Smad2 and Smad4 transcription factors, concurrent with activation of transcription. Chromatin immunoprecipitation analyses combined with siRNA-mediated knockdown indicate that Smad protein binding and the reduction of nucleosome occupancy at the AFP distal promoter is dependent on Foxa1. In addition to facilitating transcription factor binding, Foxa1 is also associated with histone modifications related to active gene expression. Acetylation of lysine 9 on histone H3, a mark that is associated active transcription, is dependent on Foxa1, while methylation of H3K4, also associated with active transcription, is independent of Foxa1. I propose that Foxa1 potentiates a region of chromatin to respond to Smad proteins, leading to active expression of AFP.^ These studies demonstrate one mechanism whereby a transcription factor can alter the accessibility of additional transcription factors to chromatin, by altering nucleosome positions. Specifically, Foxa1 exposes DNA so that Smad4 can bind to its regulatory element and activate transcription of the tumor-marker gene AFP.^

Investigating the structure and form of condom decisional balance in an alternative school sample using confirmatory factor analysis

Teen pregnancy is a continuing problem, bringing with it a host of associated health and social risks. Alternative school students are especially at risk, but are historically under-represented in research. This is especially problematic in that instruments are needed to guide effective intervention development, but psychometrics for these instruments cannot be assumed when used in new populations. Decisional balance from the transtheoretical model offers a framework for understanding condom decision making, but has not been tested with alternative school students. Using responses from 640 subjects from Safer Choices 2 (a school-based HIV/STD/pregnancy prevention program implemented in 10 urban, southwestern alternative schools), a decisional balance scale for condom use was examined. A two-factor, mildly correlated model fit the data well. Tests of invariance examined scale functioning within gender and racial/ethnic groups. The underlying structure varied slightly based on subgroup, but on a practical level the impact on the use of scales was minimal. The structure and loadings were invariant across experimental condition. The pro scale was associated with a lower probability of having engaged in unprotected sexual behavior for sexually active subjects, and this association remained significant while controlling for demographic variables. The con scale did not show a significant association with engagement in unprotected sexual behaviors. Limitations and directions for future research were also discussed.^

Molecular mechanism by which the Escherichia coli nucleoid occlusion factor, SlmA, keeps cytokinesis in check

Cell division or cytokinesis is one of the most fundamental processes in biology and is essential for the propagation of all living species. In Escherichia coli, cell division occurs by ingrowth of the membrane envelope at the cell center and is orchestrated by the FtsZ protein. FtsZ self-assembles into linear protofilaments in a GTP dependent manner to form a cytoskeletal scaffold called the Z-ring. The Z-ring provides the framework for the assembly of the division apparatus and determines the site of cytokinesis. The total amount of FtsZ molecules in a cell significantly exceeds the concentration required for Z-ring formation. Hence, Z-ring formation must be highly regulated, both temporally and spatially. In particular, the assembly of Z-rings at the cell poles and over chromosomal DNA must be prevented. These inhibitory roles are played by two key regulatory systems called the Min and nucleoid occlusion (NO) systems. In E. coli, Min proteins oscillate from pole to pole; the net result of this oscillatory process is the formation of a zone of FtsZ inhibition at the cell poles. However, the replicated nucleoid DNA near the midcell must also be protected from bisection by the Z-ring which is ensured by NO. A protein called SlmA was shown to be the effector of NO in E. coli. SlmA was identified in a screen designed to isolate mutations that were lethal in the absence of Min, hence the name SlmA (synthetic lethal with a defective Min system). Furthers SlmA was shown to bind DNA and localize to the nucleoid fraction of the cell. Additionally, light scattering experiments suggested that SlmA interacts with FtsZ-GTP and alters its polymerization properties. Here we describe studies that reveal the molecular mechanism by which SlmA mediates NO in E. coli. Specifically, we determined the crystal structure of SlmA, identified its DNA binding site specificity, and mapped its binding sites on the E. coli chromosome by chromatin immuno-precipitation experiments. We went on to determine the SlmA-FtsZ structure by small angle X-ray scattering and examined the effect of SlmA-DNA on FtsZ polymerization by electron microscopy. Our combined data show how SlmA is able to disrupt Z-ring formation through its interaction with FtsZ in a specific temporal and spatial manner and hence prevent nucleoid guillotining during cell division.

Poly(A)-binding protein-interacting protein 1 binds to eukaryotic translation initiation factor 3 to stimulate translation.

Poly(A)-binding protein (PABP) stimulates translation initiation by binding simultaneously to the mRNA poly(A) tail and eukaryotic translation initiation factor 4G (eIF4G). PABP activity is regulated by PABP-interacting (Paip) proteins. Paip1 binds PABP and stimulates translation by an unknown mechanism. Here, we describe the interaction between Paip1 and eIF3, which is direct, RNA independent, and mediated via the eIF3g (p44) subunit. Stimulation of translation by Paip1 in vivo was decreased upon deletion of the N-terminal sequence containing the eIF3-binding domain and upon silencing of PABP or several eIF3 subunits. We also show the formation of ternary complexes composed of Paip1-PABP-eIF4G and Paip1-eIF3-eIF4G. Taken together, these data demonstrate that the eIF3-Paip1 interaction promotes translation. We propose that eIF3-Paip1 stabilizes the interaction between PABP and eIF4G, which brings about the circularization of the mRNA.

Molecular mechanism by which the nucleoid occlusion factor, SlmA, keeps cytokinesis in check.

In Escherichia coli, cytokinesis is orchestrated by FtsZ, which forms a Z-ring to drive septation. Spatial and temporal control of Z-ring formation is achieved by the Min and nucleoid occlusion (NO) systems. Unlike the well-studied Min system, less is known about the anti-DNA guillotining NO process. Here, we describe studies addressing the molecular mechanism of SlmA (synthetic lethal with a defective Min system)-mediated NO. SlmA contains a TetR-like DNA-binding fold, and chromatin immunoprecipitation analyses show that SlmA-binding sites are dispersed on the chromosome except the Ter region, which segregates immediately before septation. SlmA binds DNA and FtsZ simultaneously, and the SlmA-FtsZ structure reveals that two FtsZ molecules sandwich a SlmA dimer. In this complex, FtsZ can still bind GTP and form protofilaments, but the separated protofilaments are forced into an anti-parallel arrangement. This suggests that SlmA may alter FtsZ polymer assembly. Indeed, electron microscopy data, showing that SlmA-DNA disrupts the formation of normal FtsZ polymers and induces distinct spiral structures, supports this. Thus, the combined data reveal how SlmA derails Z-ring formation at the correct place and time to effect NO.

Human TOB, an antiproliferative transcription factor, is a poly(A)-binding protein-dependent positive regulator of cytoplasmic mRNA deadenylation.

In mammalian cells, mRNA decay begins with deadenylation, which involves two consecutive phases mediated by the PAN2-PAN3 and the CCR4-CAF1 complexes, respectively. The regulation of the critical deadenylation step and its relationship with RNA-processing bodies (P-bodies), which are thought to be a site where poly(A)-shortened mRNAs get degraded, are poorly understood. Using the Tet-Off transcriptional pulsing approach to investigate mRNA decay in mouse NIH 3T3 fibroblasts, we found that TOB, an antiproliferative transcription factor, enhances mRNA deadenylation in vivo. Results from glutathione S-transferase pull-down and coimmunoprecipitation experiments indicate that TOB can simultaneously interact with the poly(A) nuclease complex CCR4-CAF1 and the cytoplasmic poly(A)-binding protein, PABPC1. Combining these findings with those from mutagenesis studies, we further identified the protein motifs on TOB and PABPC1 that are necessary for their interaction and found that interaction with PABPC1 is necessary for TOB's deadenylation-enhancing effect. Moreover, our immunofluorescence microscopy results revealed that TOB colocalizes with P-bodies, suggesting a role of TOB in linking deadenylation to the P-bodies. Our findings reveal a new mechanism by which the fate of mammalian mRNA is modulated at the deadenylation step by a protein that recruits poly(A) nuclease(s) to the 3' poly(A) tail-PABP complex.

The processing of human pro-tumor necrosis factor

Human pro-TNF-$\alpha$ is a 26 kd type II transmembrane protein, and it is the precursor of 17 kd mature TNF. Pro-TNF release mature from its extracellular domain by proteolytic cleavage between resideu Ava ($-$1) and Val (+1). Both forms of TNF are biologically active and the native form of mature TNF is a bell-shaped trimer. The structure of pro-TNF was studied both in intact cell system and in an in vitro translation system by chemical crosslinking. We found that human pro-TNF protein exist as a trimer in intact cells (LPS-induced THP-1 cells and TNF cDNA transfected COS-3 cells) and this trimeric structure is assembled intracellularly, possibly in the ER. By analysis several deletion mutants, we observed a correlation between expression of pro-TNF cytotoxicity in a juxtacrine fashion and detection of the trimer, suggesting the trimeric structure is very important for its biologic activity. With a series of deletion mutants in the linking domain, we found that the small deletion did not block the cleavage and large deletion did regardless of the presence or absence of the native cleavage site, suggesting that the length of the residues between the plasma membrane and the base of the trimer determines the rate of the cleavage, possibly by blocking the accessibility of the cleavage enzyme to its action site. Our data also suggest that the native cleavage site is not sufficient for the release of mature TNF and alternative cleavage site(s) exists. ^

Protein quaternary structure determination using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and chemical crosslinking

A means of analyzing protein quaternary structure using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI MS) and chemical crosslinking was evaluated. Proteins of known oligomeric structure, as well as monomeric proteins, were analyzed to evaluate the method. The quaternary structure of proteins of unknown or uncertain structure was investigated using this technique. The stoichiometry of recombinant E. coli carbamoyl phosphate synthetase and recombinant human farnesyl protein transferase were determined to be heterodimers using glutaraldehyde crosslinking, agreeing with the stoichiometry found for the wild type proteins. The stoichiometry of the gamma subunit of E. coli DNA polymerase III holoenzyme was determined in solution without the presence of other subunits to be a homotetramer using glutaraldehyde crosslinking and MALDI MS analysis. Chi and psi subunits of E. coli DNA polymerase III subunits appeared to form a heterodimer when crosslinked with heterobifunctional photoreactive crosslinkers.^ Comparison of relative % peak areas obtained from MALDI MS analysis of crosslinked proteins and densitometric scanning of silver stained sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) gels showed excellent qualitative agreement for the two techniques, but the quantitative analyses differed, sometimes significantly. This difference in quantitation could be due to SDS-PAGE conditions (differential staining, loss of sample) or to MALDI MS conditions (differences in ionization and/or detection). Investigation of pre-purified crosslinked monomers and dimers recombined in a specific ratio revealed the presence of mass discrimination in the MALDI MS process. The calculation of mass discrimination for two different MALDI time-of-flight instruments showed the loss of a factor of approximately 2.6 in relative peak area as the m/z value doubles over the m/z range from 30,000 to 145,000 daltons.^ Indirect symmetry was determined for tetramers using glutaraldehyde crosslinking with MALDI MS analysis. Mathematical modelling and simple graphing allowed the determination of the symmetry for several tetramers known to possess isologous D2 symmetry. These methods also distinguished tetramers that did not fit D2 symmetry such as apo-avidin. The gamma tetramer of E. coli DNA polymerase III appears to have isologous D2 symmetry. ^