The effect of a suppressed rad52 mutation on the suppression of rad6 by srs2

We have cloned a suppressor of a temperature-sensitive rad52 allele and found it to be a mutation in PUP1, a gene encoding a protease subunit of the 20s proteasome. This identity prompted us to examine the interrelationship among PUP1, RAD52, SRS2 and RAD6 because srs2 mutations not only suppress some rad52 mutations but also suppress deletions of rad6, a gene encoding a protein in the ubiquination-dependent proteolysis pathway. We have found that while srs2 suppresses the UV sensitivity of rad6 in the presence of RAD52, srs2 cannot suppress rad6 when the temperature-sensitive allele of rad52 is present. This inability of srs2 to suppress rad6 is irrespective of the incubation temperature or whether pup1 is suppressing the temperature-sensitive rad52 mutation.