THE RAD16 GENE OF SCHIZOSACCHAROMYCES-POMBE - A HOMOLOG OF RAD1 GENE OF SACCHAROMYCES-CEREVISIAE

The rad10, rad16, rad20, and swi9 mutants of the fission yeast Schizos accharomyces pombe, isolated by their radiation sensitivity or abnorma l mating-type switching, have been shown cvn previously to be allelic. We have cloned DNA correcting the UV sensitivity or mating-type switc hing phenotype of these mutants and shown that the correcting DNA is e ncompassed in a single open reading frame. The gene, which we will ref er to as rad16, is approximately 3 kb in length, contains seven intron s, and encodes a protein of 892 amino acids. It is not essential for v iability of S. pombe. The predicted protein is the homolog of the Sacc haromyces cerevisiae RAD1 protein, which is involved in an early step in excision-repair of UV damage from DNA. The approximately 30% sequen ce identity between the predicted proteins from the two yeasts is dist ributed throughout the protein. Two-hybrid experiments indicate a stro ng protein-protein interaction between the products of the rad16 and s wi10 genes of S. pombe, which mirrors that reported for RAD1 and RADIO in S. cerevisiae. We have identified the mutations in the four allele s of rad16. They mapped to the N-terminal (rad10), central (rad20), an d C-terminal (rad16 and swi9) regions. The rad10 and rad20 mutations a re in the splice donor sequences of introns 2 and 4, respectively. The plasmid correcting the UV sensitivity of the rad20 mutation,vas missi ng the sequence corresponding to the 335 N-terminal amino acids of the predicted protein. Neither smaller nor larger truncations were, howev er, able to correct its UV sensitivity.