Ebp2p, yeast homologue of a human protein that interacts with Epstein-Barr virus nuclear antigen 1, is required for pre-rRNA processing and ribosomal subunit assembly.
BACKGROUND
A defect in the secretory pathway causes the transcriptional repression of both rRNA and ribosomal protein genes in Saccharomyces cerevisiae, suggesting a coupling of ribosome synthesis and plasma membrane synthesis. Rrs1p, an essential nuclear protein, is required for the secretory response.


RESULTS
EBP2, encoding the yeast homologue of a human protein that interacts with Epstein-Barr virus Nuclear Antigen 1, was cloned in a two-hybrid screen using RRS1 as a bait. The rrs1-1 mutation, which produces Rrs1p without the C-terminal half and causes a defect in the secretory response, almost abolished the interaction with Ebp2p. Ebp2p is essential for growth and is mainly localized in the nucleolus. The effects of Ebp2p depletion on ribosome biogenesis is quite similar to that of Rrs1p depletion; in the Ebp2p-depleted cells, the rate of pre-rRNA processing is slower, and significantly less mature 25S rRNA is produced compared to those in wild-type cells. The polysome pattern indicates that Ebp2p-depletion causes a decrease of 80S monosomes and polysomes, an accumulation of 40S subunits, and the appearance of half-mer polysomes.


CONCLUSIONS
Ebp2p is required for the maturation of 25S rRNA and 60S subunit assembly. Ebp2p may be one of the target proteins of Rrs1p for executing the signal to regulate ribosome biogenesis.
Tsujii
R
R
Department of Molecular Biotechnology, Graduate School of Advanced Sciences of Matter, Hiroshima University, Kagamiyama 1-4-1, Higashi-Hiroshima 739-8527, Japan.
Miyoshi
K
K
Tsuno
A
A
Matsui
Y
Y
Toh-e
A
A
Miyakawa
T
T
Mizuta
K
K
D015152:Blotting, Northern; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D002466:Cell Nucleolus / Q000502:physiology; D019309:Epstein-Barr Virus Nuclear Antigens / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D008715:Methionine / Q000737:chemistry; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010957:Plasmids; D011132:Polyribosomes / Q000378:metabolism; D012322:RNA Precursors / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000096:biosynthesis*; D016601:RNA-Binding Proteins; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins; D020798:Two-Hybrid System Techniques
D002352:Carrier Proteins; C432687:EBNA1BP2 protein, human; C499008:EBP2 protein, S cerevisiae; D019309:Epstein-Barr Virus Nuclear Antigens; D009687:Nuclear Proteins; D012322:RNA Precursors; D012335:RNA, Ribosomal; D016601:RNA-Binding Proteins; C485770:RRS1 protein, S cerevisiae; C405526:RRS1 protein, human; D029701:Saccharomyces cerevisiae Proteins; C065039:RNA, ribosomal, 25S; D008715:Methionine