CONSTRUCTION OF A PULSED-FIELD MAP AROUND D3S3 USING PARTIALLY DEMETHYLATED DNA

Heavy methylation of restriction sites in the relevant chromosomal reg ion can be a major problem in the construction of a long-range restric tion map. In the region around the locus D3S3 there appeared to be few accessible restriction sites. Therefore, we cultured cells in the pre sence of 5-azacytidine and used the partially demethylated DNA to cons truct a relatively detailed restriction map spanning approximately 1 M b. Using partially demethylated DNA is a recommendable approach when a genome region appears inaccessible for pulsed-field analysis because excessively long restriction fragments are obtained.