Modulation of repair and fixation of UV-induced damage and its effects on mutagenesis in yeast.

Modulation of repair of UVC-induced damage under different post-irradiation nutritional conditions and its effects on mutagenesis were studied in stationary phase cells of diploid strain D7 of Saccharomyces cerevisiae. Reverse mutation and gene conversion frequencies at ILV and TRP locus were measured in the respective omission media. It was observed that post-irradiation (150 x 10(-3) J/m2) repair in presence of (i) 2-deoxy-D-glucose (2-DG, 10 mM) resulted in decreased surviving fraction (56 +/- 5%) and increase in frequencies of revertants and gene convertants (122 +/- 10% & 132 +/- 14% respectively), (ii) yeast extract enhanced the frequency of revertants to a large extent (204 +/- 18%) and (iii) yeast extract and 2-DG together further increased the frequencies of revertants (304 +/- 15%) and gene convertants (151 +/- 12%); when compared with irradiated controls in phosphate buffer glucose; the observed changes being statistically significant (P < 0.05, Student's t test). These results indicate that (i) 2DG reduces the error-free DNA repair in yeast, (ii) yeast extract increases error-prone DNA repair and thus, in combination with 2-DG, further promotes mutagenesis.