Delayed rRNA Processing Results in Significant Ribosome Biogenesis and Functional Defects

Abstract

mof6-1 was originally isolated as a recessive mutation in Saccharomyces cerevisiae which promoted increased efficiencies of programmed −1 ribosomal frameshifting and rendered cells unable to maintain the killer virus. Here, we demonstrate that mof6-1 is a unique allele of the histone deacetylase RPD3, that the deacetylase function of Rpd3p is required for controlling wild-type levels of frameshifting and virus maintenance, and that the closest human homolog can fully complement these defects. Loss of the Rpd3p-associated histone deacetylase function, either by mutants of rpd3 or loss of the associated gene product Sin3p or Sap30p, results in a delay in rRNA processing rather than in an rRNA transcriptional defect. This results in production of ribosomes having lower affinities for aminoacyl-tRNA and diminished peptidyltransferase activities. We hypothesize that decreased rates of peptidyl transfer allow ribosomes with both A and P sites occupied by tRNAs to pause for longer periods of time at −1 frameshift signals, promoting increased programmed −1 ribosomal frameshifting efficiencies and subsequent loss of the killer virus. The frameshifting defect is accentuated when the demand for ribosomes is highest, suggesting that rRNA posttranscriptional modification is the bottleneck in ribosome biogenesis.

ACKNOWLEDGMENTS

A.M. and J.L.B. contributed equally to this work.

We thank Andrew Vershon, Michael Hampsey, Lenore Neigeborn, and S. L. Shreiber for strains and clones and for helping to provide critical insights.

This work was supported by a grant to J.D.D. from the NIH (GM58859). J.L.B. was supported in part by a training grant from the NIH (T32 AI51967).