Variation in the rate of DNA chain growth through the S phase in HeLa cells

At five to six hours after the beginning of the S phase, the over-all rate of HeLa cell DNA synthesis is about five times as great as in early S cells. This is due both to an increased number of growing points and to a doubling of the average rate of growth along replicons. The pattern of replicon operation in HeLa cells is changed when the “thymidine double-block” method is used to induce synchrony.