Rat RL23a ribosomal protein efficiently competes with its Saccharomyces cerevisiae L25 homologue for assembly into 60 S subunits.
The large subunit protein RL23a from rat liver ribosomes shows 62% sequence identity with the primary rRNA-binding ribosomal protein L25 from Saccharomyces cerevisiae. In vitro binding studies indicated that both r-proteins are able to recognise the L25 binding site on yeast 25 S rRNA and its structural homologue on mammalian 28 S rRNA with equal efficiency. To determine whether the two r-proteins are also functionally equivalent in vivo, a single plasmid-borne copy of either the wild-type L25 gene or the RL23a cDNA, driven by the L25 promoter, was introduced into a yeast strain in which the chromosomal L25 gene is under control of the glucose-repressible GALI-10 promoter. No difference in growth rate could be detected between the two types of transformants when cultured on glucose-based medium. In cells that co-express epitope-tagged versions of L25 and RL23a from single-copy genes, approximately 35% of the 60 S subunits contained the heterologous protein as determined by Western analysis. This value could be increased to 55% by overexpressing RL23a using a multi-copy plasmid. These data demonstrate that rat RL23a can act as a highly efficient substitute for its yeast counterpart in the assembly of functional yeast ribosomes even in the presence of the endogenous L25 protein.
Jeeninga
R E
RE
Department of Biochem. and Mol. Biol., IMBW BioCentrum Amsterdam Vrije Universiteit, The Netherlands.
Venema
J
J
Raué
H A
HA
D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D008099:Liver / Q000378:metabolism; D008969:Molecular Sequence Data; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012269:Ribosomal Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
D011994:Recombinant Proteins; D012269:Ribosomal Proteins; C079497:Rpl23a protein, rat; C031127:ribosomal protein L25