SPECIFIC VARIANTS OF H1 HISTONE REGULATE CPG METHYLATION IN EUKARYOTIC DNA

Upon HPLC fractionation of human placenta or calf thymus H1 histone pr eparations, only some fractions enriched in the H1e-c variants were ab le to exert a severe inhibition on in vitro enzymatic DNA methylation. These fractions, though similar to the other variants in interacting with genomic DNA, were also the only ones which could bind CpG-rich ds -oligodeoxyribonucleotides (oligos). Both the 6-CpG ds-oligo and the D NA purified from chromatin fractions enriched in 'CpG islands' were go od competitors for the binding of H1e-c to the G(me)CpG ds-oligo. This ability to bind any DNA sequence and to suppress the enzymatic methyl ation in any sequence containing CpG dinucleotides suggests, for these particular H1 variants, a possible role in maintaining CpG island DNA and linker DNA at low methylation levels.