Mapping of ssDNA Nicks within dsDNA Genomes by Two-dimensional Gel Electrophoresis

DNA molecules within chromosomes undergo constant, dynamic changes yet maintain the integrity of the primary DNA sequence. DNA replication, adjustment of helical density, resolution of catenenes, repair of DNA damage, and homologous recombination each involve breakage and religation of the phosphate backbone of the double helix. Although the analysis of dsDNA breaks is facile, the analysis of ssDNA nicks is not. The principal impediment is that conventional, one-dimensional electrophoresis methods cannot readily detect ssDNA nicks in the context of dsDNA breaks. We therefore developed a two dimensional (native/denaturing) gel electrophoresis approach to map the positions of ssDNA nicks. Analysis of cohesive ends of lambda phage DNA, UV-nicked DNA molecules, and DNA treated with ssDNA nicking endonuclease N-BbvcIB revealed that the method can detect and map with precision the positions of ssDNA nicks. Titration experiments revealed the ability to detect and quantitate nicked DNA molecules present at a frequency of 1% of total DNA molecules. This method can be used both to scan rapidly through large regions of the genome of interest and to map with high-resolution the location of ssDNA nicks in populations of dsDNA molecules. It is of utility for the analysis of ssDNA nicks involved in a variety of chromosomal processes

Does social exclusion motivate interpersonal reconnection? Resolving the "porcupine problem"

Evidence from 6 experiments supports the social reconnection hypothesis, which posits that the experience of social exclusion increases the motivation to forge social bonds with new sources of potential affiliation. Threat of social exclusion led participants to express greater interest in making new friends, to increase their desire to work with others, to form more positive impressions of novel social targets, and to assign greater rewards to new interaction partners. Findings also suggest potential boundary conditions to the social reconnection hypothesis. Excluded individuals did not seem to seek reconnection with the specific perpetrators of exclusion or with novel partners with whom no face-to-face interaction was anticipated. Furthermore, fear of negative evaluation moderated responses to exclusion such that participants low in fear of negative evaluation responded to new interaction partners in an affiliative fashion, whereas participants high in fear of negative evaluation did not