BIOCHIM1E, 1982, 64, 815-821. CNRS symposium, May 1982 - TOULOUSE Inducible responses to DNA damages Error-prone replication of ultraviolet-irradiated Simian Virus 40 in carcinogen-treated monkey kidney cells. Alain SARASIN <>, Frangois BOURRE and Annie BENOIT. Institut de Recherches Scientifiques sur le Cancer, B.P. 8 - 94802 Villejuif Cedex, France. R~sum6. Darts Ie but d'analyser le mdcanisme moldcu- laire de la mutagdnkse dans les cellules de mammi- fkres traitdes par des cancdrogknes, nous avons mis au point un test analytique en utilisant des mu- tants thermosensibles du virus SV40 et des cellules de rein de singe en culture. Ce systbme exp&imen- tal est particuli~rement addquat pour ddtecter la prdsence de processus de r@aration inductibles par les canc&og~nes. Les rdsultats montrent que le traitement de cellules par les rayons ultraviolets, la N-acdtoxy- acdtylaminofluorbne ou la mitomycine C augmente la mutagdn~se du virus SV40 prdalablement irradid aux UV. Cette mutag~nbse est mesurde par la rd- version d'une mutation thermosensible vers un phdnotype thermordsistant. Cette augmentation de la mutagdnbse n' est pas observ6e si le virus n' a pas dtd irradid, ce qui suggbre que les mutations que nous ddtectons sont essentiellement dues ?t la prd- sence de ldsions sur le DNA viral. L' analyse mold- culaire des gdnomes des virus rdvertants indique que le phdnotype r£verse est obtenu soit par une mutation ponctuelle, soit par un rdarrangement du DNA viral dans la zone du site de la mutation ts. L'ensembIe de nos rdsultats peut s'interprdter par l'induction dans les cellules traitdes par un cancdrogbne, d'un processus de rdplication erronde capable de mieux rdpliquer le DNA viral irradid aux UV, mais au prix d'une mutagdnkse dlevde. Cette activitd est un candidat potentiel pouvant faire partie des fonctions SOS induites chez les mammifkres. Mots-cl~s : r~paration SOS / mutag~n~se / SV40 / eanc~rog~nes. Summary. To analyze the molecular mechanism of muta- genesis in carcinogen-treated mammalian cells, we developed a model system composed of various simian virus 40 (SV40) mutants as a biological probe to detect inducible DNA repair and muta- genesis in carcinogen-treated monkey kidney cells (CVI-P). Results have shown that treatment of cells with UV-light, acetoxy-acetyl-aminofluorene, or mito- mycin C, increases the mutagenesis of UV-irradia- ted SV40 ts mutant measured as a reversion fre- quency from a thermosensitive phenotype toward a thermoresistant phenotype. This increased muta- genesis is not observed in the case of undamaged virus indicating that we are looking at targeted mutagenesis. The molecular analysis of several re- vertant genomes indicates that some DNA rearran- gements may occur in the revertant genomes but in some cases the reversion site is a single base- pair substitution located at positions different from the original thermosensitive mutation, which is still present. The general interpretation of our results leads to the conclusion that carcinogen treatment of monkey cells activates some kind of error-prone replication mode able to better replicate UV- damaged templates but leading to a higher level of mutagenesis. This activity may represent a SOS- like function in mammalian cells. Key-words : SOS repair / mutagenesis / SV40 / carcinogens. Introduction. Almost all carcinogens have been shown to be mutagens and mutations have been strongly invol- ved in the first steps of carcinogenesis. The mecha- <> To whom all correspondence shouM be addressed. nisms of mutation induction have been particularly well studied in E. coli, where it has been shown that the blockage of a replication fork by a DNA- damaging treatment, induces a series of closely related effects, called SOS functions [1-3]. These