INDUCTION OF THE GENES RAD54 AND RNR2 BY VARIOUS DNA-DAMAGING AGENTS IN SACCHAROMYCES-CEREVISIAE

The relationship between the induction of the genes RAD54 and RNR2 and the induction and repair of specific DNA lesions was studied in the y east Saccharomyces cerevisiae using Rad54-lacZ and RNR2-lacZ fusion st rains. Gene induction was followed by measuring beta-galactosidase act ivity. At comparable levels of furocoumarin-DNA photoadducts, RAD54 wa s more effectively induced by bifunctional than by monofunctional furo coumarins indicating that mixtures of monoadducts (MA) and interstrand cross-links (CL) provide a stronger inducing signal than MA. RNR2 ind uction kinetics were measured in relation to cell growth and survival responses after treatment with the furocoumarins 8-methoxypsoralen (8- MOP), 5-methoxypsoralen (5-MOP), 3-carbethoxypsoralen (3-CPs), 7-methy lpyrido[3,4-c]psoralen (MePyPs) and 4,4',6-trimethylangelicin (TMA), b enzo[a]pyrene (B(a)P and 1,6-dioxapyrene (1,6-DP) plus UVA, 254 nm UV radiation and cobalt-60 gamma-radiation. Induction of RNR2 took place during the DNA repair period before resumption of cell growth and clea rly increased with increasing equitoxic dose levels. Treatments with f urocoumarin plus 365 nm radiation (UVA) and 254 nm (UV) radiation were effective inducers whereas gene induction was relatively weak after g amma-radiation and absent after the induction of oxidative damage by B (a)P and 1,6-DP and UVA. The results suggest that it is the specific p rocessing of different DNA lesions that determines the potency of the induction signal. Apparently, DNA lesions such as CL, and probably als o closely located MA or pyrimidine dimers in opposite DNA strands invo lving the formation of double-strand breaks as repair intermediates, a re most effective inducers.