NOL11, implicated in the pathogenesis of North American Indian childhood cirrhosis, is required for pre-rRNA transcription and processing.
The fundamental process of ribosome biogenesis requires hundreds of factors and takes place in the nucleolus. This process has been most thoroughly characterized in baker's yeast and is generally well conserved from yeast to humans. However, some of the required proteins in yeast are not found in humans, raising the possibility that they have been replaced by functional analogs. Our objective was to identify non-conserved interaction partners for the human ribosome biogenesis factor, hUTP4/Cirhin, since the R565W mutation in the C-terminus of hUTP4/Cirhin was reported to cause North American Indian childhood cirrhosis (NAIC). By screening a yeast two-hybrid cDNA library derived from human liver, and through affinity purification followed by mass spectrometry, we identified an uncharacterized nucleolar protein, NOL11, as an interaction partner for hUTP4/Cirhin. Bioinformatic analysis revealed that NOL11 is conserved throughout metazoans and their immediate ancestors but is not found in any other phylogenetic groups. Co-immunoprecipitation experiments show that NOL11 is a component of the human ribosomal small subunit (SSU) processome. siRNA knockdown of NOL11 revealed that it is involved in the cleavage steps required to generate the mature 18S rRNA and is required for optimal rDNA transcription. Furthermore, abnormal nucleolar morphology results from the absence of NOL11. Finally, yeast two-hybrid analysis shows that NOL11 interacts with the C-terminus of hUTP4/Cirhin and that the R565W mutation partially disrupts this interaction. We have therefore identified NOL11 as a novel protein required for the early stages of ribosome biogenesis in humans. Our results further implicate a role for NOL11 in the pathogenesis of NAIC.
Department of Genetics, Yale University School of Medicine, New Haven, Connecticut, United States of America.
Emily F
EF
Freed
José-Luis
JL
Prieto
Kathleen L
KL
McCann
Brian
B
McStay
Susan J
SJ
Baserga
D001665:Binding Sites; D002466:Cell Nucleolus / Q000235:genetics / Q000378:metabolism; D002648:Child; D017124:Conserved Sequence; D015723:Gene Library; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D007198:Indians, North American / Q000235:genetics*; D008103:Liver Cirrhosis / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D009154:Mutation; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012322:RNA Precursors; D012337:RNA, Ribosomal, 18S / Q000235:genetics* / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D012261:Ribonucleoproteins / Q000235:genetics* / Q000378:metabolism; D012270:Ribosomes / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D020798:Two-Hybrid System Techniques
C576804:NOL11 protein, human; D009687:Nuclear Proteins; D012322:RNA Precursors; D012337:RNA, Ribosomal, 18S; D034741:RNA, Small Interfering; D012261:Ribonucleoproteins; C470475:UTP4 protein, human