Hypomethylation of human heterochromatin detected by restriction enzyme nick translation.

Using the restriction enzymes MspI and HpaII in the nick translation procedure it has been shown that decondensation of the paracentric heterochromatin of chromosome 9 during human spermatogenesis is associated with hypomethylation of the DNA sequences in this domain. Somatic cells treated with 5'-azacytidine also showed decondensation of centromeric heterochromatin. In this instance, however, hypomethylation is detected both in the extended heterochromatin at the centromeres and in the euchromatin of the chromosome arms.