Analysis of two human pre-ribosomal factors, bystin and hTsr1, highlights differences in evolution of ribosome biogenesis between yeast and mammals.
Recent studies reveal that maturation of the 40S ribosomal subunit precursors in mammals includes an additional step during processing of the internal transcribed spacer 1 (ITS1), when compared with yeast Saccharomyces cerevisiae, even though the protein content of the pre-40S particle appears to be the same. Here, we examine by depletion with siRNA treatment the function of human orthologs of two essential yeast pre-ribosomal factors, hEnp1/bystin and hTsr1. Like their yeast orthologs, bystin is required for efficient cleavage of the ITS1 and further processing of this domain within the pre-40S particles, whereas hTsr1 is necessary for the final maturation steps. However, bystin depletion leads to accumulation of an unusual 18S rRNA precursor, revealing a new step in ITS1 processing that potentially involves an exonuclease. In addition, pre-40S particles lacking hTsr1 are partially retained in the nucleus, whereas depletion of Tsr1p in yeast results in strong cytoplasmic accumulation of pre-40S particles. These data indicate that ITS1 processing in human cells may be more complex than currently envisioned and that coordination between maturation and nuclear export of pre-40S particles has evolved differently in yeast and mammalian cells.
Carron
Coralie
C
Université de Toulouse, UPS, Laboratoire de Biologie Moléculaire Eucaryote and CNRS, LBME, F-31000 Toulouse, France.
O'Donohue
Marie-Françoise
MF
Choesmel
Valérie
V
Faubladier
Marlène
M
Gleizes
Pierre-Emmanuel
PE
D021581:Active Transport, Cell Nucleus; D005075:Biological Evolution; D015815:Cell Adhesion Molecules / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006367:HeLa Cells; D006801:Humans; D009687:Nuclear Proteins / Q000737:chemistry; D012322:RNA Precursors / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012335:RNA, Ribosomal / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000502:physiology*; D054682:Ribosome Subunits, Small, Eukaryotic / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid
C112245:BYSL protein, human; D015815:Cell Adhesion Molecules; C104527:ENP1 protein, S cerevisiae; D009687:Nuclear Proteins; D012322:RNA Precursors; D012335:RNA, Ribosomal; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; C555735:Tsr1 protein, human
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