Depression of reverse transcriptase activity by hybridoma supernatants: a potential problem in screening for retroviral contamination.

Murine hybridoma cell lines generally produce retroviral particles (type A and/or type C), often in large numbers. We have measured reverse transcriptase activity in the supernatant of some 30 hybridoma lines of murine origin and found that the observed activity expressed as pmoles of [3H]-dGMP incorporated into an acid insoluble polymer, is frequently much lower than would be expected from the amount of retrovirus seen by electron microscopy in the corresponding cells. We demonstrate that this reduction is due to the presence of a nuclease which degrades the high molecular weight product but is not due to a change in the reverse transcriptase activity. This nuclease activity may be associated with mycoplasma contamination of the cell lines.