Induction of cellular DNA synthesis by defective human cytomegalovirus.

The results presented in this paper show that virus stocks enriched for defective particles are more effective in stimulating cellular DNA synthesis than are stocks relatively free of defective particles. Several lines of evidence support this conclusion: (1) Low levels of UV irradiation enhance the ability of standard virus stocks to stimulate cellular DNA synthesis. (2) Three different stocks derived from individual plaques (which presumably contain very few defective particles) and passaged only twice at low multiplicity, were found to be poor inducers of cellular DNA synthesis. (3) Stocks of virions obtained after serial undiluted passage which were shown to be enriched for defective particles were quite effective in stimulating cellular DNA synthesis.