Structure, function and DNA composition of Saccharomyces cerevisiae chromatin loops

Recent localization of cohesin association regions along the yeast chromatin fibre suggests that compositional variability of DNA in yeast is related to the function and organization of the chromosomal loops. The bases of the loops, where the chromatin fibre is attached to the chromosomal axis, are AT-rich, bind cohesin, and are flanked by genes transcribed convergently. The hotspots of meiotic recombination are mainly found in the GC-rich parts of the loops, 'external' with respect to the chromosomal axis, frequently in the vicinity of the promoters of divergently transcribed genes. There are two possible reasons why the regions of the hotspots of recombination were enriched in GC content during evolution. One is a biased repair of recombination intermediates, and the second is a selective advantage due to an increased chromatin accessibility, which may have the carriers of GC-enriched alleles over the carriers of AT-rich alleles.