DNA replication in human diploid cells of different origin

DNA-fiber autoradiography has been used to study the replication of chromosomal DNA from cultured human cells of different origin. In normal embryonic fibroblasts, brain cells, heart cells, hepatocytes, and post-natal fibroblasts and lymphocytes the rate of DNA replication in a single fork varies from 0.2 to 1.0 micrometer/min with a mean of about 0.6 micrometer/min; and the size of replication units varies from 80 to 400 micrometer with a mean of about 200 micrometer. The data obtained indicate that in cultured somatic cells of various tissues of the same organism, the rate of DNA replication and the number of functioning replication units are practically the same.