Rio2p, an evolutionarily conserved, low abundant protein kinase essential for processing of 20 S Pre-rRNA in Saccharomyces cerevisiae.
Saccharomyces cerevisiae Rio2p (encoded by open reading frame Ynl207w) is an essential protein of unknown function that displays significant sequence similarity to Rio1p/Rrp10p. The latter was recently shown to be an evolutionarily conserved, predominantly cytoplasmic serine/threonine kinase whose presence is required for the final cleavage at site D that converts 20 S pre-rRNA into mature 18 S rRNA. A data base search identified homologs of Rio2p in a wide variety of eukaryotes and Archaea. Detailed sequence comparison and in vitro kinase assays using recombinant protein demonstrated that Rio2p defines a subfamily of protein kinases related to, but both structurally and functionally distinct from, the one defined by Rio1p. Failure to deplete Rio2p in cells containing a GAL-rio2 gene and direct analysis of Rio2p levels by Western blotting indicated the protein to be low abundant. Using a GAL-rio2 gene carrying a point mutation that reduces the kinase activity, we found that depletion of this mutant protein blocked production of 18 S rRNA due to inhibition of the cleavage of cytoplasmic 20 S pre-rRNA at site D. Production of the large subunit rRNAs was not affected. Thus, Rio2p is the second protein kinase that is essential for cleavage at site D and the first in which the processing defect can be linked to its enzymatic activity. Contrary to Rio1p/Rrp10p, however, Rio2p appears to be localized predominantly in the nucleus.
Geerlings
Torsten H
TH
Section of Biochemistry and Molecular Biology, Instituut Moleculair-Biologische Wetenschappen, BioCentrum Amsterdam, Vrije Universiteit, de Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.
Faber
Alex W
AW
Bister
Milena D
MD
Vos
Jan C
JC
Raué
Hendrik A
HA
D001483:Base Sequence; D002455:Cell Division; D017124:Conserved Sequence; D019143:Evolution, Molecular; D005838:Genotype; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015345:Oligonucleotide Probes; D010802:Phylogeny; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D012322:RNA Precursors / Q000235:genetics*; D012323:RNA Processing, Post-Transcriptional; D012331:RNA, Fungal / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000145:classification* / Q000166:cytology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D009687:Nuclear Proteins; D015345:Oligonucleotide Probes; D012322:RNA Precursors; D012331:RNA, Fungal; D029701:Saccharomyces cerevisiae Proteins; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; C473025:Rio2 protein, S cerevisiae