Study of DNA synthesis in chromatin isolated from HeLa cells.

When incubated in vitro, HeLa cell chromatin can synthesize DNA at rate comparable to that observed with isolated nuclei. The in vitro DNA synthetic activity of chromatin reflects DNA synthesis in intact cells since chromatin from cells in S phase are several times more active thatn preparations derived from mitotic cells. The requirements for the synthesis of DNA by chromatin preparations are also similar to those of isolated nuclei and the size of the DNA pieces made in both systems is roughly comparable. The chromatin system offers several advantages not available with isolated nuclei. Chromatin will synthesize DNA for a much longer time than isolated nuclei so that larger amounts of DNA can be synthesized in vitro In addition, although chromatin has its own endogenous ability to synthesize DNA, it is markedly stimulated by the presence of exogenously added HeLa cell DNA polymerase alpha, beta, and gamma, and, thus, may provide a new template system for the study of DNA synthesis.