GENETIC ORGANIZATION OF THE STRUCTURAL GENES FOR NITRATE REDUCTASE (TN5)

Nitrate reductase in Escherichia coli is a membrane-bound anaerobic enzyme that is repressed by oxygen and induced by nitrate. The genetic organization of the structural genes for the two larger subunits of nitrate reductase ((alpha) and (beta)) was determined by immunoprecipitation analysis of the formation of these proteins in nitrate reductase-deficient mutants resulting from transposon Tn5 mutagenesis. The results suggested that the genes encoding the (alpha) and (beta) subunits (narG and H) were arranged in an operon with transcription in the direction promoter(--->)(alpha)(--->)(beta). Segments of the chromosome containing the Tn5 inserts from several of the mutants were cloned into plasmid pBR322 and the positions of the transposons determined by restriction mapping. The Tn5 insertion sites were localized on two contiguous EcoRI fragments spanning about 6.6 kilobases of DNA. The narI gene (proposed to encode the (gamma) subunit) was positioned immediately downstream from the (beta)-gene (narH) by Southern analysis of Tn10 insertions into the narI locus. A Tn10 insertion into the narK locus, proposed to encode a nitrate-sensitive repressor of other anaerobic enzymes, was located about 1.5 kilobases upstream from the narGHI operon promoter. The narL locus, proposed to encode a nitrate-sensitive positive regulator of the narGHI operon and known to be genetically linked to the other nar genes, was demonstrated to lie outside a 19.3-kilobase region of the chromosome which encompasses the other nar genes. The physical limit of the narGHI promoter was defined by studying the effect of Tn5 insertions into a hybrid plasmid containing the functional operon. The points of origin of the coding regions for the (alpha) and (beta) genes were deduced by alignment of the chromosomal map of Tn5 insertion sites with the sizes of (alpha) and (beta) subunit fragments produced by plasmids carrying these Tn5 inserts in the nar operon. The coding region for the (alpha) subunit (143,000 daltons) begins about 250 nucleotides downstream from the deduced limit of the promoter region and includes about 4.0 kilobases of DNA; the region encoding (beta) (60,000 daltons) lies immediately downstream from the (alpha)-gene and is approximately 1.6 kilobases in length. The adjacent region encoding the (gamma) subunit (19,000 daltons) is approximately 0.5 kilobase in length. ^

AN ANALYSIS OF THE GENERAL WELL-BEING OF BLACKS AND WHITES

The importance of race as a factor in mental health status has been a topic of controversy. This study reviews the history of research in this area and examines racial variances in the relationship between selected socio-demographic variables and general well-being. The study also examines the appropriateness of an additive versus an interactive statistical model for this investigation.^ The sample consists of 6,913 persons who completed the General Well-Being Schedules as administered in the detailed component of the first National Health and Nutrition Examination Survey (NHANES I) conducted by the National Center for Health Statistics between April, 1971 and October, 1975. The sampling design is a multistage, probability sample of clusters of persons in area based segments. Of the 6,913 persons, 873 are Black.^ Unlike other recent community based mental health studies, this study revealed significant differences between the general well-being of Blacks and Whites. Blacks continued to exhibit significantly lower levels of well-being even after adjustments were made for income, education, marital status, sex, age and place of residence. Statistical interaction was found between race and sex with Black females reporting lower levels of well-being than either Black or White males or their White female counterparts.^ The study includes a detailed review of the NHANES I sample design. It is shown that selected aspects of the design make it difficult to render appropriate national comparisons of Black-White differences. As a result conclusions pertaining to these differences based on NHANES I may be of questionable validity. ^