Abstract
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.
Highlights
Yeast ribosome consists of 4 rRNAs and 78 ribosomal proteins (RP).1 The amounts of the components are coordinately regulated corresponding to cell growth mainly at the level of transcription [1, 2]
Genetic analysis showed that the mutation is recessive; when the mutant cells were crossed to parental sly1 cells of the opposite mating type, RP genes RPL28 and RPL3 were significantly repressed at the restrictive temperature
These results suggest that Rrs1p and Rpl11p have a function in the same signaling pathway in response to a secretory defect and that protein-protein interaction of the two proteins may be important in the signaling
Summary
Yeast ribosome consists of 4 rRNAs and 78 ribosomal proteins (RP). The amounts of the components are coordinately regulated corresponding to cell growth mainly at the level of transcription [1, 2]. We demonstrated that Rrs1p was essential for growth, localized in the nucleus, and required for ribosome biogenesis, especially for 25 S rRNA maturation and 60 S ribosomal subunit assembly [6]. This suggested that the mechanism of the signaling in response to a secretory defect was closely linked to normal regulation of ribosome biogenesis. Rpl11p shows physical interaction with Rrs1p, which may have a central role for the signaling in response to a secretory defect These results suggest that 60 S ribosomal subunit assembly machinery containing Rpl11p and Rrs1p is essential for the signaling
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