CENP-A-containing nucleosomes: easier disassembly versus exclusive centromeric localization.

CENP-A is a histone variant that replaces conventional H3 in nucleosomes of functional centromeres. We report here, from reconstitutions of CENP-A- and H3-containing nucleosomes on linear DNA fragments and the comparison of their electrophoretic mobility, that CENP-A induces some positioning of its own and some unwrapping at the entry-exit relative to canonical nucleosomes on both 5 S DNA and the alpha-satellite sequence on which it is normally loaded. This steady-state unwrapping was quantified to 7(+/-2) bp by nucleosome reconstitutions on a series of DNA minicircles, followed by their relaxation with topoisomerase I.

Mapping candidate hotspots of meiotic recombination in segments of human DNA cloned in the yeast Saccharomyces cerevisiae.

The hotspots of meiotic recombination in the human genome can be localized by genetic techniques. The resolution of these techniques is in the range of kilobases and depends on the density of the physical markers identifying allelic variants of the chromosomal loci. We thought it would be interesting to localize these sites with higher resolution.

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.

Nuclease-hypersensitive chromatin formed by a CpG island in human DNA cloned as an artificial chromosome in yeast.

CpG islands are mostly unmethylated GC-, and CpG-rich chromosomal segments overlapping promoter sequences in all housekeeping and many tissue-specific genes in vertebrates. Typically, these islands show an open chromatin structure, low in histone H1 and rich in acetylated histones. We have previously found that the island-like CGCG-rich sites in human DNA are hypersensitive to DNase I upon cloning in Saccharomyces cerevisiae.