THE EFFECTS OF THREE PSO GENES ON INDUCED MUTAGENESIS: A NOVEL CLASS OF MUTATIONALLY DEFECTIVE YEAST

C. Cassier ¹, R. Chanet ¹, J. A. P. Henriques ¹, and E. Moustacchi ¹

¹ Institut Curie, Biologie, Bâtiment 110, Centre Universitaire, 91405 Orsay, France

Reverse and forward mutation, induced by photoaddition of 8-methoxypsoralen (8-MOP) and 3-carbethoxypsoralen (3-CPs) or ultraviolet light (UV), are reduced in three pso mutants of Saccharomyces cerevisiae. The pso1–1 strain exhibits a lower frequency of spontaneous reversion (antimutator) and is almost entirely unaffected by the three agents in both the haploid and diploid states. The pso2–1 strain demonstrates very reduced frequencies of 8-MOP and 3-CPs plus 365 nm radiation-induced mutations in happloid and diploid cells. UV-induced mutations are slightly reduced, whereas survival is almost normal. The pso3–1 strain is mutable by 8-MOP and 3-CPs photoaddition only in the low-dose range. After UV treatment, survival of pso3–1 is nearly normal, whereas the frequencies of induced mutants are diminished as compared to the normal PSO⁺. An analogue of adenine, 6-N-hydroxyaminopurine, is capable of inducing reversions in wild type, as well as in pso and rad6–1 mutant strains, indicating that this drug may act as a direct mutagen in yeast. The comparison of photoaddition of the bifunctional agent (8-MOP) to that of the monofunctional one (3-CPs) confirms that cross-links, as well as monoadditions, are mutagenic in S. cerevisiae. Repair, of the recombinational type, taking place in diploid cells or in haploid cells in G2 phase leads to higher survival, but appears to be error-free.

This article has been cited by other articles:

				X. Zhong, P. Garg, C. M. Stith, S. A. N. McElhinny, G. E. Kissling, P. M. J. Burgers, and T. A. Kunkel The fidelity of DNA synthesis by yeast DNA polymerase zeta alone and with accessory proteins Nucleic Acids Res., October 18, 2006; 34(17): 4731 - 4742. [Abstract] [Full Text] [PDF]

				L. J. Barber, T. A. Ward, J. A. Hartley, and P. J. McHugh DNA Interstrand Cross-Link Repair in the Saccharomyces cerevisiae Cell Cycle: Overlapping Roles for PSO2 (SNM1) with MutS Factors and EXO1 during S Phase Mol. Cell. Biol., March 15, 2005; 25(6): 2297 - 2309. [Abstract] [Full Text] [PDF]

				B. A. Kunz, K. Ramachandran, and E. J. Vonarx DNA Sequence Analysis of Spontaneous Mutagenesis in Saccharomyces cerevisiae Genetics, April 1, 1998; 148(4): 1491 - 1505. [Abstract] [Full Text] [PDF]