LOS1P, INVOLVED IN YEAST PRE-TRANSFER-RNA SPLICING, POSITIVELY REGULATES MEMBERS OF THE SOL GENE FAMILY

To understand the role of Los1p in pre-tRNA splicing, we sought los1 m ulticopy suppressors. We found SOLI that suppresses both point and nul l LOS1 mutations. Since, when fused to the Ga14p DNA-binding domain, L os1p activates transcription, we tested whether Los1p regulates SOLI. We found that los1 mutants have depleted levels of SOLI mRNA and Sol1p . Thus, LOS1 appears to positively regulate SOLI. SOLI belongs to a mu ltigene family with at least two additional members, SOL2 and SOW. Sol proteins have extensive similarity to an unusual group of glucose-6-p hosphate dehydrogenases. As the similarities are restricted to areas s eparate from the catalytic domain, these G6PDs may have more than one function. The SOL family appears to be unessential since cells with a triple disruption of all three SOL genes are viable. SOL gene disrupti ons negatively affect tRNA-mediated nonsense suppression and the sever ity increases with the number of mutant SOL genes. However, tRNA level s do not vary with either multicopy SOL genes or with SOL disruptions. Therefore, the Sol proteins affect tRNA expression/function at steps other than transcription or splicing. We propose that LOS1 regulates g ene products involved in tRNa expression/function as well as pre-tRNA splicing.