Survival, DNA synthesis and ribosomal RNA transcription in monkey kidney cells treated by formaldehyde

Separate cultures of CV-1 cells were exposed for 15 min to 1-16 mM formaldehyde (FA) at various time intervals before labeling with [3H]uridine. The labeled RNA extracted from whole cells was analyzed by polyacrylamide gel electrophoresis. Results indicated that FA produced transcription-terminating lesions in DNA which depressed RNA synthesis, gave rise to shortened RNA chains and modified the expression of transcription-linked genes. These lesions were efficiently repaired since a recovery of RNA transcription, with disappearance of the initially observed alterations, rapidly occurred during post-treatment incubation of cells. Cycloheximide (5 micrograms/ml) strongly inhibited this recovery, whereas fluorodeoxyuridine (10(-5) M) was without effect. The rate of semi-conservative DNA synthesis, measured autoradiographically by thymidine incorporation, as well as the number of cells performing DNA replication, fell to zero after 15-min exposure to FA concentrations greater than 2 mM. Both parameters recovered subnormal levels during a 24-h incubation after treatment with FA concentration up to 8 mM, in agreement with the high survival observed. Unscheduled DNA synthesis was not detectable during the restoration of DNA and RNA synthesis.