Genes encoding ribosomal proteins Rps0A/B of Saccharomyces cerevisiae interact with TOM1 mutants defective in ribosome synthesis

The Saccharomyces cerevisiae RPS0A/B genes encode proteins of the 40S ribos omal subunit that are required for the maturation of 18S rRNA. We show here that the RPS0 genes interact genetically with TOM1. TOM1 encodes a member of the hect-domain-containing E3 ubiquitin-protein ligase family that is re quired for growth at elevated temperatures. Mutant alleles of the RPS0 and TOM1 genes have synergistic effects on cell growth at temperatures permissi ve for TOM1 mutants. Moreover, the growth arrest of TOM1 mutants at elevate d temperatures is partially suppressed by overexpression of RPSOA/B. Strain s with mutant alleles of TOM1 are defective in multiple steps in rRNA proce ssing, and interactions between RPSOA/B and TOM1 stem, in Dart, from their roles in the maturation of ribosomal subunits. Ribosome synthesis is theref ore included among the cellular processes governed by members of the hect-d omain-containing E3 ubiquitin-protein ligase family.