THE PAD1(-S PROTEASOME IN FISSION YEAST() GENE ENCODES A SUBUNIT OF THE 26)

We have isolated a fission yeast mutant, mfs5-1, in a screen for mutat ions that confer both methyl 5-benzimidazolecarbamate resistance (MBCR ) and temperature sensitivity (ts) on Schizosaccharomyces pombe. This screen has previously isolated mutations in the 26 S proteasome subuni ts Mts2, Mts3, and Mts4. We show that the mutation in the mts5-1 strai n occurs in the pad1(+) gene. pad1(+) was originally isolated on a mul ticopy plasmid that was capable of conferring staurosporine resistance on a wild type strain. mts5-1/pad1-1 has a similar phenotype to 26 S proteasome mutants previously isolated in the same screen and we show that Pad1 interacts genetically with two of these subunits, Mts3 and M ts4. In this study we describe the identification of Pad1 as a subunit of the 26 S proteasome in fission yeast.