Qsr1p, a 60S ribosomal subunit protein, is required for joining of 40S and 60S subunits.
QSR1 is a recently discovered, essential Saccharomyces cerevisiae gene, which encodes a 60S ribosomal subunit protein. Thirty-one unique temperature-sensitive alleles of QSR1 were generated by regional codon randomization within a conserved 20-amino-acid sequence of the QSR1-encoded protein. The temperature-sensitive mutants arrest as viable, large, unbudded cells 24 to 48 h after a shift to 37 degrees C. Polysome and ribosomal subunit analysis by velocity gradient centrifugation of lysates from temperature-sensitive qsr1 mutants and from cells in which Qsr1p was depleted by down regulation of an inducible promoter revealed the presence of half-mer polysomes and a large pool of free 60S subunits that lack Qsr1p. In vitro subunit-joining assays and analysis of a mutant conditional for the synthesis of Qsr1p demonstrate that 60S subunits devoid of Qsr1p are unable to join with 40S subunits whereas 60S subunits that contain either wild-type or mutant forms of the protein are capable of subunit joining. The defective 60S subunits result from a reduced association of mutant Qsr1p with 60S subunits. These results indicate that Qsr1p is required for ribosomal subunit joining.
Eisinger
D P
DP
Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
Dick
F A
FA
Trumpower
B L
BL
D002470:Cell Survival; D015536:Down-Regulation; D005656:Fungal Proteins / Q000096:biosynthesis / Q000378:metabolism*; D016296:Mutagenesis; D011132:Polyribosomes / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012269:Ribosomal Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D013696:Temperature
D005656:Fungal Proteins; C093333:RPL10 protein, S cerevisiae; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins