BINDING OF HISTONE H1E-C VARIANTS TO CPG-RICH DNA CORRELATES WITH THEINHIBITORY EFFECT ON ENZYMATIC DNA METHYLATION

Within the H1 histone family, only some fractions enriched in the H1e- c variants are effective in causing a marked inhibition, in vitro, of enzymic DNA methylation and, in gel retardation and Southwestern blot experiments, in binding double-stranded (ds) CpG-rich oligonucleotides . Both the 6-CpG ds-oligonucleotide and the DNA purified from chromati n fractions enriched in 'CpG islands' are good competitors for the bin ding of H1e-c to 6-meCpG ds-oligonucleotide. Because of their ability to bind any DNA sequence and to suppress the enzymic methylation in an y sequence containing CpG dinucleotides, these particular H1 variants could play some role in maintaining linker DNA at low methylation leve ls and even in preserving the unmethylated state of the CpG-rich islan ds which characterize the promoter regions of housekeeping genes.