Different DNA End Configurations Dictate Which NHEJ Components Are Most Important for Joining Efficiency

The nonhomologous DNA end-joining (NHEJ) pathway is a key mechanism for repairing dsDNA breaks that occur often in eukaryotic cells. In the simplest model, these breaks are first recognized by Ku, which then interacts with other NHEJ proteins to improve their affinity at DNA ends. These include DNA-PK$_{cs}$ and Artemis for trimming the DNA ends; DNA polymerase μ and λ to add nucleotides; and the DNA ligase IV complex to ligate the ends with the additional factors, XRCC4 (X-ray repair cross-complementing protein 4), XLF (XRCC4-like factor/Cernunos), and PAXX (paralog of XRCC4 and XLF). $\textit{In vivo}$ studies have demonstrated the degrees of importance of these NHEJ proteins in the mechanism of repair of dsDNA breaks, but interpretations can be confounded by other cellular processes. $\textit{In vitro}$ studies with NHEJ proteins have been performed to evaluate the nucleolytic resection, polymerization, and ligation steps, but a complete system has been elusive. Here we have developed a NHEJ reconstitution system that includes the nuclease, polymerase, and ligase components to evaluate relative NHEJ efficiency and analyze ligated junctional sequences for various types of DNA ends, including blunt, 5' overhangs, and 3' overhangs. We find that different dsDNA end structures have differential dependence on these enzymatic components. The dependence of some end joining on only Ku and XRCC4·DNA ligase IV allows us to formulate a physical model that incorporates nuclease and polymerase components as needed.National Institutes of Health, Cancer Research UK Program Grant IDs: C6/A11224, C6946/A14492), Wellcome Trust (Grant IDs: WT092096, WT093167

Gender differences in musical aptitude, rhythmic ability and motor performance in preschool children

Most of the preschool curricula involve integrated movement activities that combine music, rhythm and locomotor skills. The purpose of the current study was to examine whether there are any differences between boys and girls at the age of five concerning their musical aptitude, rhythmic ability and performance in gross motor skills. Ninety-five preschool children participated in the study (50 girls and 45 boys). The measures used were the Primary Measures of Music Audiation, the High/ Scope Rhythmic Competence Analysis Test and the Gross Motor Development test 2. The results revealed no significant gender differences in musical aptitude and gross motor skills performance, whereas girls outperformed boys in four of the six movements of rhythmic ability test. Considering that rhythmic competence is strongly inter-related with children's motor coordination, the concluding suggestion for the preschool physical education curriculum is to incorporate specific rhythmic activities (like Orff, Dalcroze and dance) in order to overcome the boys' performance deficiency. © 2005 Taylor & Francis Group Ltd