Pol5 is an essential ribosome biogenesis factor required for 60S ribosomal subunit maturation in Saccharomyces cerevisiae

RNA. 2019 Nov;25(11):1561-1575. doi: 10.1261/rna.072116.119. Epub 2019 Aug 14.


In Saccharomyces cerevisiae, more than 250 trans-acting factors are involved in the maturation of 40S and 60S ribosomal subunits. The expression of most of these factors is transcriptionally coregulated to ensure correct ribosome production under a wide variety of environmental and intracellular conditions. Here, we identified the essential nucleolar Pol5 protein as a novel trans-acting factor required for the synthesis of 60S ribosomal subunits. Pol5 weakly and/or transiently associates with early to medium pre-60S ribosomal particles. Depletion of and temperature-sensitive mutations in Pol5 result in a deficiency of 60S ribosomal subunits and accumulation of half-mer polysomes. Both processing of 27SB pre-rRNA to mature 25S rRNA and release of pre-60S ribosomal particles from the nucle(ol)us to the cytoplasm are impaired in the Pol5-depleted strain. Moreover, we identified the genes encoding ribosomal proteins uL23 and eL27A as multicopy suppressors of the slow growth of a temperature-sensitive pol5 mutant. These results suggest that Pol5 could function in ensuring the correct folding of 25S rRNA domain III; thus, favoring the correct assembly of these two ribosomal proteins at their respective binding sites into medium pre-60S ribosomal particles. Pol5 is homologous to the human tumor suppressor Myb-binding protein 1A (MYBBP1A). However, expression of MYBBP1A failed to complement the lethal phenotype of a pol5 null mutant strain though interfered with 60S ribosomal subunit biogenesis.

Keywords: MYBBP1A; nucleolus; pre-rRNA processing; ribosomal proteins uL23 and eL27; ribosome biogenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Nucleus / metabolism
  • Cytoplasm / metabolism
  • DNA-Directed DNA Polymerase / metabolism*
  • RNA Processing, Post-Transcriptional
  • Ribosome Subunits, Large, Eukaryotic / metabolism*
  • Ribosomes / metabolism*
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins / metabolism*


  • Saccharomyces cerevisiae Proteins
  • DNA-Directed DNA Polymerase
  • POL5 protein, S cerevisiae