Saccharomyces cerevisiae Ribosomal Protein L26 Is Not Essential for Ribosome Assembly and Function

Abstract

Ribosomal proteins play important roles in ribosome biogenesis and function. Here, we study the evolutionarily conserved L26 in Saccharomyces cerevisiae , which assembles into pre-60S ribosomal particles in the nucle(ol)us. Yeast L26 is one of the many ribosomal proteins encoded by two functional genes. We have disrupted both genes; surprisingly, the growth of the resulting rpl26 null mutant is apparently identical to that of the isogenic wild-type strain. The absence of L26 minimally alters 60S ribosomal subunit biogenesis. Polysome analysis revealed the appearance of half-mers. Analysis of pre-rRNA processing indicated that L26 is mainly required to optimize 27S pre-rRNA maturation, without which the release of pre-60S particles from the nucle(ol)us is partially impaired. Ribosomes lacking L26 exhibit differential reactivity to dimethylsulfate in domain I of 25S/5.8S rRNAs but apparently are able to support translation in vivo with wild-type accuracy. The bacterial homologue of yeast L26, L24, is a primary rRNA binding protein required for 50S ribosomal subunit assembly in vitro and in vivo . Our results underscore potential differences between prokaryotic and eukaryotic ribosome assembly. We discuss the reasons why yeast L26 plays such an apparently nonessential role in the cell.

Ribosome Biogenesis in the YeastSaccharomyces cerevisiae

“…Consistent with this work, most r-proteins copurify with the earliest pre-rRNAs and assembly factors (Ferreira-Cerca et al 2007;Babiano and De La Cruz 2010;Babiano et al 2012;Jakovljevic et al 2012;Gamalinda et al 2013). However, the order of assembly of r-proteins relative to each other cannot be distinguished at any higher resolution by existing methods.…”

“…Nonessential r-proteins also may play important roles in ribosome biogenesis or function (Babiano et al 2012;Baronas-Lowell and Warner 1990;Briones et al 1998;DeLabre et al 2002;Peisker et al 2008;Remacha et al 1995;Sachs and Davis 1990;Steffen et al 2012;Yu and Warner 2001). Fifty-nine of the 79 yeast r-proteins are encoded by two paralogous genes (Simoff et al 2009).…”

A hierarchical model for assembly of eukaryotic 60S ribosomal subunit domains

“…More recently, a refined in vivo assembly map was put forward by Chen and Williamson (2013) that largely corresponds to the Nierhaus map (Rohl and Nierhaus 1982). Our collective studies on yeast RPLs (Babiano et al 2012;Jakovljevic et al 2012;Gamalinda et al 2013;Ohmayer et al 2013) show the following differences from bacterial large subunit assembly: First, while incorporation of bacterial RPLs occurs via distinct assembly groups, most yeast RPLs are present in early assembly intermediates but differ in the step of assembly for which they are required and become more stably assembled in a sequential fashion. Second, several assembly relationships observed in bacterial RPLs are not found for their eukaryotic homologs (Supplemental Fig.…”

“…Knowing these final endpoints of RP localization provides a strategic platform to investigate the connection between spatial and temporal aspects of ribosome biogenesis. Most RPs assemble with preribosomes early in the biogenesis pathway (Kruiswijk et al 1978;Ferreira-Cerca et al 2007;Babiano and de la Cruz 2010;Babiano et al 2012;Gamalinda et al 2013;Ohmayer et al 2013). As the nascent subunits mature, the association of RPs with pre-rRNA is strengthened by dynamic rearrangement of initial protein-RNA encounter complexes (Ferreira-Cerca et al 2007;Adilakshmi et al 2008;Ohmayer et al 2013).…”

Identification of the binding site of Rlp7 on assembling 60S ribosomal subunits in Saccharomyces cerevisiae

“…We tested for potential interactions between the three A 3 factors that bind to ITS2 (Rlp7, Nop15, and Cic1) and other assembly factors and r-proteins implicated in 27SA 2 (Brx1, Ebp2), 27SA 3 (Pwp1, Nop7, Ytm1, Erb1, Rrp1, Has1, Rrp17, Rat1, Rai1, L7, L8), or 27SB (L17, L26, L35, L37, Nsa2, Rrs1, Rpf2, Nog2, Nop2, Nip7, L11, Spb4, Dbp10, Tif6, Rlp24, Mak11, Nog1) pre-rRNA processing, as well as other r-proteins that contact domain I (L15, L25) (Henry et al 1994;Emery et al 2004;Zhang et al 2004;Oeffinger et al 2009;Ben-Shem et al 2011;Granneman et al 2011;Sahasranaman et al 2011;Babiano et al 2012;Jakovljevic et al 2012;Shimoji et al 2012;Talkish et al 2012;Gamalinda et al 2013). Only 11 of the 210 potential pair-wise two-hybrid interactions tested were positive, confirming the specificity of the assay ( Fig.…”