Creating a dynamic picture of the sliding clamp during T4 DNA polymerase holoenzyme assembly by using fluorescence resonance energy transfer

The coordinated assembly of the DNA polymerase (gp43), the sliding clamp (gp45), and the clamp loader (gp44/62) to form the bacteriophage T4 DNA polymerase holoenzyme is a multistep process. A partially opened toroid-shaped gp45 is loaded around DNA by gp44/62 in an ATP-dependent manner. Gp43 binds to this complex to generate the holoenzyme in which gp45 acts to topologically link gp43 to DNA, effectively increasing the processivity of DNA replication. Stopped-flow fluorescence resonance energy transfer was used to investigate the opening and closing of the gp45 ring during holoenzyme assembly. By using two site-specific mutants of gp45 along with a previously characterized gp45 mutant, we tracked changes in distances across the gp45 subunit interface through seven conformational changes associated with holoenzyme assembly. Initially, gp45 is partially open within the plane of the ring at one of the three subunit interfaces. On addition of gp44/62 and ATP, this interface of gp45 opens further in-plane through the hydrolysis of ATP. Addition of DNA and hydrolysis of ATP close gp45 in an out-of-plane conformation. The final holoenzyme is formed by the addition of gp43, which causes gp45 to close further in plane, leaving the subunit interface open slightly. This open interface of gp45 in the final holoenzyme state is proposed to interact with the C-terminal tail of gp43, providing a point of contact between gp45 and gp43. This study further defines the dynamic process of bacteriophage T4 polymerase holoenzyme assembly.

Antigenic peptides containing large PEG loops designed to extend out of the HLA-A2 binding site form stable complexes with class I major histocompatibility complex molecules.

Recognition of peptides bound to class I major histocompatibility complex (MHC) molecules by specific receptors on T cells regulates the development and activity of the cellular immune system. We have designed and synthesized de novo cyclic peptides that incorporate PEG in the ring structure for binding to class I MHC molecules. The large PEG loops are positioned to extend out of the peptide binding site, thus creating steric effects aimed at preventing the recognition of class I MHC complexes by T-cell receptors. Peptides were synthesized and cyclized on polymer support using high molecular weight symmetrical PEG dicarboxylic acids to link the side chains of lysine residues substituted at positions 4 and 8 in the sequence of the HLA-A2-restricted human T-lymphotrophic virus type I Tax peptide. Cyclic peptides promoted the in vitro folding and assembly of HLA-A2 complexes. Thermal denaturation studies using circular dichroism spectroscopy showed that these complexes are as stable as complexes formed with antigenic peptides.

Taking The 'Sport' Out of Sports Parenting: Toward A Theory of Sport Related Parent-Child Communication Competency

Research has shown that over-emphasis on winning is the number one reason why approximately seventy percent of the forty million children who participate in youth sports will quit by age 13. This study utilized a constructivist grounded theory approach to investigate the role of parent-child communication within the context of youth sports. A total of 22 athletes and 20 parents were recruited through a Western university to discuss messages exchanged during youth sport participation. The results suggest that the delineation between messages of support and pressure is largely dependent on discursive work done by both parent and child. Parents who employed competent communicative strategies to avoid miscommunications regarding participation and sports goals were able to provide support and strengthen the relationship despite pressurized situations. The present study frames the youth sport dilemma within a developing conceptualization of communicative (in)competence and offers theoretical implications for sport related parent-child communication competency (SRPCCC).

The Psychology of Adolescent Out-of Wedlock Pregnancy and Childbearing

Illegitimate adolescent pregnancy creates a variety of problems, beginning with the difficult decision about whether or not to terminate the pregnancy. If the pregnancy is carried to term, choices follow regarding marriage or single parenthood and keeping or relinquishing the child. All of these choices involve consequences for the adolescent, many of them negative ones. This paper examines the problem of out-of-wedlock teen pregnancy and its possible psychological sources. It also introduces a method for analyzing the psychology of unwed teen pregnancy and childbearing and reviews the literature on the subject by this method. NOTE: Approvals page submitted to digital archive lacks signatures

Out of the ordinary : Anne Ryan and collage

Anne Ryan (1889-1954) was an active member of New York’s vibrant avant-garde art community during the tumultuous period marked by World War II. Ryan participated in the famed 1951 “Ninth Street Show,” and was an early member of Betty Parsons’s legendary stable of artists. She is not widely known today, however, and her influence is rarely acknowledged. Ryan is primarily known for her abstract collages—works that are frequently linked to Abstract Expressionism.

The emergence of classical behaviour in magnetic adatoms

A wide class of nanomagnets shows striking quantum behaviour, known as quantum spin tunnelling (QST): instead of two degenerate ground states with opposite magnetizations, a bonding-antibonding pair forms, resulting in a splitting of the ground-state doublet with wave functions linear combination of two classically opposite magnetic states, leading to the quenching of their magnetic moment. Here we study how QST is destroyed and classical behaviour emerges in the case of magnetic adatoms, where, contrary to larger nanomagnets, the QST splitting is in some instances bigger than temperature and broadening. We analyze two different mechanisms for the renormalization of the QST splitting: Heisenberg exchange between different atoms, and Kondo exchange interaction with the substrate electrons. Sufficiently strong spin-substrate and spin-spin coupling renormalize the QST splitting to zero allowing the environmental decoherence to eliminate superpositions between classical states, leading to the emergence of spontaneous magnetization. Importantly, we extract the strength of the Kondo exchange for various experiments on individual adatoms and construct a phase diagram for the classical to quantum transition.

Controlled rippling of graphene via irradiation and applied strain modify its mechanical properties: a nanoindentation simulation study

Ripples, present in free standing graphene, have an important influence in the mechanical behavior of this two-dimensional material. In this work we show through nanoindentation simulations, how out-of-plane displacements can be modified by strain resulting in softening of the membrane under compression and stiffening under tension. Irradiation also induces changes in the mechanical properties of graphene. Interestingly, compressed samples, irradiated at low doses are stiffened by the irradiation while samples under tensile strain do not show significant changes in their mechanical properties. These simulations indicate that vacancies, produced by the energetic ions, cannot be the ones directly responsible for this behavior. However, changes in roughness induced by the momentum transferred from the energetic ions to the membrane, can explain these differences. These results provide an alternative explanation to recent experimental observations of stiffening of graphene under low dose irradiation, as well as paths to tailor the mechanical properties of this material via applied strain and irradiation.

Confession of students for walking out of commons, April 1807

This document, signed by 108 students, contains a confession for their part in the 1807 student rebellion. Students were required to sign this confession in order to avoid expulsion.