The rhp6⁺ gene of Schizosaccharomyces pombe: A structural and functional homolog of the RAD6 gene from the distantly related yeast Saccharomyces cerevisiae

The RAD6 gene of Saccharomyces cerevisiae encodes a ubiquitin conjugating enzyme and is required for DNA repair, DNA-damage-induced mutagenesis and sporulation. Here, we show that RAD6 and the rhp6⁺ gene from the distantly related yeast Schizosaccharomyces pombe share a high degree of structural and functional homology. The predominantly acidic carboxyl-terminal 21 amino acids present in the RAD6 protein are absent in the rhp6⁺-encoded protein; otherwise, the two proteins are very similar, with 77% identical residues. Like rad6, null mutations of the rhp6⁺ gene confer a defect in DNA repair, UV mutagenesis and sporulation, and the RAD6 and rhp6⁺ genes can functionally substitute for one another. These observations suggest that functional interactions between RAD6 (rhp6⁺) protein and other components of the DNA repair complex have been conserved among eukaryotes.