Differential repair of UV damage in Saccharomyces cerevisiae is cell cycle dependent.

Abstract

In the yeast Saccharomyces cerevisiae the transcriptionally active MATα locus is repaired preferentially to the inactive HLMα locus after UV irradiation. Here we analysed the repair of both loci after irradiating yeast cells at different stages of the mitotic cell cycle. In all stages repair of the active MATα locus occurs at a rate of 30% removal of dimers per hour after a UV dose of 60 J/m2. The inactive HLMα is repaired as efficiently as MATα following irradiation in G2 whereas repair of HLMα is less efficient in the other stages. Thus differential repair is observed in G1 and S but not in G2. Apparently, in G2 a chromatin structure exists in which repair does not discriminate between transcriptionally active and inactive DNA or, alternatively, an additional repair mechanism might exist which is only operational during G2.