Nonvirionic inhibitor of DNA synthesis in human embryo fibroblast cell cultures infected with rubella virus

Human embryo fibroblast cell cultures (RU-I) infected with virulent and attentuated strains of rubella virus of treated with a cell extract form infected and from control cultures have been studies in respect of their mitotic activity by evaluating the (3-H) thymidine uptake by autoradiography. The results show the presence in infected cell cultures of a nonvirionic inhibitor of DNA synthesis, which is detectable in control cell cultures too, though to a lesser degree. The relation of this inhibitor to the chalone system is so far unclear. No effect of the extracts on human chromosome pattern was observed. Attempts of biochemical characterization by fractionation of 14-C-labeled extracts on polyacrylamide gel followed by autoradiography were unsuccessful.