Effect of HpaII and MspI restriction endonucleases on chronic myelogenous leukemia chromosomes. Detection of CpG dinucleotide demethylation in situ.

The restriction endonucleases HpaII and MspI both cleave the nucleotide sequence CCGG, but the action of HpaII is inhibited if the internal cytosine is methylated. HpaII and MspI were used on fixed chromosomes from bone marrow cells of individuals suffering from chronic myelogenous leukemia and healthy individuals. We found that MspI acts with the same efficiency on all chromosome samples, whereas HpaII extracts more DNA from the chromosomes of leukemic individuals than from the chromosomes of nonleukemic individuals. We postulate that demethylation of cytosine in the CpG dinucleotide of leukemic cell DNA accounts for our findings.