J. Biol. Chem., Vol. 262, Issue 10, 4472-4476, Apr, 1987
DNase I site mapping and micrococcal nuclease digestion of pachytene chromatin reveal novel structural features
BJ Rao and MR Rao
A comparison of the DNase I digestion products of the 32P-5'-end- labeled
pachytene nucleosome core particles (containing histones H2A, TH2A, X2,
H2B, TH2B, H3, and H4) and liver nucleosome core particles (containing
somatic histones H2A, H2B, H3, and H4) revealed that the cleavage sites
that are 30, 40, and 110 nucleotides away from the 5'- end are
significantly more accessible in the pachytene core particles than in the
liver core particles. These cleavage sites correspond to the region wherein
H2B interacts with the nucleosome core DNA. These results, therefore,
suggest that the histone-DNA interaction at these sites in the pachytene
core particles is weaker, possibly because of the presence of the histone
variant TH2B interacting at similar topological positions in the nucleosome
core as that of its somatic counterpart H2B. Such a loosened structure may
also be maintained even in the native pachytene chromatin since micrococcal
nuclease digestion of pachytene nuclei resulted in a higher ratio of
subnucleosomes (SN4 + SN7) to mononucleosomes than that observed in liver
chromatin.