Characterization of novel rad6/ubc2 ubiquitin-conjugating enzyme mutants in yeast

Null mutations in the RAD6/UBC2 gene encoding an E2 ubiquitin-conjugating e nzyme cause deficiencies in DNA repair, N-end-rule protein degradation, spo rulation and telomeric silencing, and alter the preferred integration posit ions for Ty1 retrotransposons. Here we selected for mutants of RAD6 that ca use a release of telomeric silencing. Some alleles retained nearly wild-typ e ability for sporulation, DNA repair and the degradation of proteins. Alte ration in Ty1 integration-site bias accompanied some of these alleles. The possibility that some mutations specifically affect binding of an unknown p rotein that works with Rad6 in its silencing role, but is not required for DNA repair or N-end-rule activity, is discussed in terms of the Rad6 crysta l structure.