DNA REPLICATION PATTERNS IN CULTURED FEMALE RAT FIBROBLASTS

Abstract

Pulse and continuous labeling procedures involving available H3 thymidine were used to determine the relative periods of DNA synthesis within general segments of the metaphase chromosomes of rat cells cultured in vitro. A strain of fibroblast cells of diploid constitution derived from a female rat of the highly inbred Lewis strain was studied and, as in a number of mammals, one of the X''s was "late-labeling". The S period''s duration was estimated to be 9 hours. Certain segments upon identifiable chromosomes showed discernible patterns of synthesis and chromosomes 19 and 29 were among the first to complete synthesis of DNA. Regions adjacent to the cnetromeres of many chromosomes were "late-labeling", suggesting that these may represent heterochromatic regions.