Isolation of the REC1 gene controlling recombination in Ustilago maydis.

Previous studies on the rec1 mutant of Ustilago maydis revealed a complex phenotype. The mutant was found to be defective in DNA repair, recombination, growth, mutagenesis, and meiosis. We cloned the REC1 gene by complementing the phenotype of the mutant using a genomic DNA library made in a replicating vector and provided proof of identity by one-step gene disruption of the wild-type (wt) REC1 locus with a mutant allele constructed in vitro. The transcript of the REC1 gene was identified as a damage-inducible 1.7-kb RNA. After UV irradiation, the level of the transcript was observed to rise ten- to 15-fold. In the rec1 mutant, the basal level of the 1.7-kb transcript was tenfold lower than in wt. In addition, a second transcript of 1.1 kb was noted in rec1-1 cells in response to DNA damage.