Nip7p Interacts with Nop8p, an Essential Nucleolar Protein Required for 60S Ribosome Biogenesis, and the Exosome Subunit Rrp43p

摘要: NIP7 encodes a conserved Saccharomyces cerevisiae nucleolar protein that is required for 60S subunit biogenesis (N. I. T. Zanchin, P. Roberts, A. DeSilva, F. Sherman, and D. S. Goldfarb, Mol. Cell. Biol. 17:5001–5015, 1997). Rrp43p second essential protein, Nop8p, were identified in two-hybrid screen as Nip7p-interacting proteins. Biochemical evidence an interaction was provided by the copurification on immunoglobulin G-Sepharose of Nip7p with A-tagged Nop8p. Cells depleted Nop8p contained reduced levels free ribosomes polysomes accumulated half-mer polysomes. Nop8p-depleted cells also 35S pre-rRNA aberrant 23S pre-rRNA. failed to accumulate either 25S or 27S rRNA, although they did synthesize significant 18S rRNA. These results indicate rRNA degraded after section containing removed. Nip7p-depleted exhibited same defects cells, except precursors. component exosome, complex 3′-to-5′ exonucleases whose subunits have been implicated 5.8S processing mRNA turnover. Whereas both green fluorescent (GFP)-Nop8p GFP-Nip7p localized nucleoli, GFP-Rrp43p throughout nucleus lesser extent cytoplasm. Distinct pools may interact exosome Nip7p, possibly cytoplasm, catalyze analogous reactions multistep process ribosome