Originally published as Genetics Published Articles Ahead of Print on June 18, 2006.

Genetics, Vol. 174, 41-55, September 2006, Copyright © 2006
doi:10.1534/genetics.106.058685

Different Mating-Type-Regulated Genes Affect the DNA Repair Defects of Saccharomyces RAD51, RAD52 and RAD55 Mutants

Maria Valencia-Burton^*,1, Masaya Oki^,2, Jean Johnson^*, Tracey A. Seier^*, Rohinton Kamakaka^,3 and James E. Haber^*,4

^* Department of Biology and Rosenstiel Center, Brandeis University, Waltham, Massachusetts 02454-9110 and Unit on Chromatin and Transcription, National Institutes of Health, Bethesda, Maryland 20892

⁴ Corresponding author: Rosenstiel Center, Brandeis University, 415 South St., Mailstop 029, Waltham, MA 02254-9110.
E-mail: haber{at}brandeis.edu

Saccharomyces cerevisiae cells expressing both a- and -mating-type (MAT) genes (termed mating-type heterozygosity) exhibit higher rates of spontaneous recombination and greater radiation resistance than cells expressing only MATa or MAT. MAT heterozygosity suppresses recombination defects of four mutations involved in homologous recombination: complete deletions of RAD55 or RAD57, an ATPase-defective Rad51 mutation (rad51-K191R), and a C-terminal truncation of Rad52, rad52-327. We investigated the genetic basis of MAT-dependent suppression of these mutants by deleting genes whose expression is controlled by the Mata1-Mat2 repressor and scoring resistance to both campothecin (CPT) and phleomycin. Haploid rad55 strains became more damage resistant after deleting genes required for nonhomologous end-joining (NHEJ), a process that is repressed in MATa/MAT cells. Surprisingly, NHEJ mutations do not suppress CPT sensitivity of rad51-K191R or rad52-327. However, rad51-K191R is uniquely suppressed by deleting the RME1 gene encoding a repressor of meiosis or its coregulator SIN4; this effect is independent of the meiosis-specific homolog, Dmc1. Sensitivity of rad52-327 to CPT was unexpectedly increased by the MATa/MAT-repressed gene YGL193C, emphasizing the complex ways in which MAT regulates homologous recombination. The rad52-327 mutation is suppressed by deleting the prolyl isomerase Fpr3, which is not MAT regulated. rad55 is also suppressed by deletion of PST2 and/or YBR052C (RFS1, rad55 suppressor), two members of a three-gene family of flavodoxin-fold proteins that associate in a nonrandom fashion with chromatin. All three recombination-defective mutations are made more sensitive by deletions of Rad6 and of the histone deacetylases Rpd3 and Ume6, although these mutations are not themselves CPT or phleomycin sensitive.

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