Normal assembly of 60 S ribosomal subunits is required for the signaling in response to a secretory defect in Saccharomyces cerevisiae.

A secretory defect leads to transcriptional repression of both ribosomal protein and rRNA genes in yeast. To elucidate the mechanism of the signaling, we previously isolated rrs mutants that were unable to respond to a secretory defect, and we cloned RRS1 encoding a nuclear protein that was required for ribosome biogenesis (Tsuno, A., Miyoshi, K., Tsujii, R., Miyakawa, T., and Mizuta, K. (2000) Mol. Cell. Biol. 20, 2066-2074). We identified duplicated genes encoding ribosomal protein L11, RPL11B as a wild-type allele complementing the rrs2 mutation, and RPL11A in two-hybrid screening using RRS1 as bait. Rpl11p was copurified with Rrs1p in immunoprecipitation analysis. Ultracentrifugation analysis revealed that Rrs1p associated fairly tightly with 60 S preribosomal subunits. These results suggest that signaling in response to a secretory defect requires the normal assembly of 60 S ribosomal subunits including Rrs1p and Rpl11p.