NSR1 Is Required for Pre-rRNA Processing and for the Proper Maintenance of Steady-State Levels of Ribosomal Subunits

Abstract

NSR1 is a yeast nuclear localization sequence-binding protein showing striking similarity in its domain structure to nucleolin. Cells lacking NSR1 are viable but have a severe growth defect. We show here that NSR1, like nucleolin, is involved in ribosome biogenesis. The nsr1 mutant is deficient in pre-rRNA processing such that the initial 35S pre-rRNA processing is blocked and 20S pre-rRNA is nearly absent. The reduced amount of 20S pre-rRNA leads to a shortage of 18S rRNA and is reflected in a change in the distribution of 60S and 40S ribosomal subunits; there is no free pool of 40S subunits, and the free pool of 60S subunits is greatly increased in size. The lack of free 40S subunits or the improper assembly of these subunits causes the nsr1 mutant to show sensitivity to the antibiotic paromomycin, which affects protein translation, at concentrations that do not affect the growth of the wild-type strain. Our data support the idea that NSR1 is involved in the proper assembly of pre-rRNA particles, possibly by bringing rRNA and ribosomal proteins together by virtue of its nuclear localization sequence-binding domain and multiple RNA recognition motifs. Alternatively, NSR1 may also act to regulate the nuclear entry of ribosomal proteins required for proper assembly of pre-rRNA particles.

18S rRNA processing requires the RNA helicase-like protein Rrp3

“…Processing, as determined by Northern analysis, of the RNA in Rrp3-depleted cells occurs as indicated in Figure 1B. A similar scheme was also determined for other genes involved in 18S rRNA processing (9,10,35). We were able to tell from the detectable intermediates that cleavages at A 0 , A 1 and A 2 were lacking (Fig.…”

“…Therefore few trans-acting factors have been identified and most by means other than their biochemical function. Several, processing proteins were identified by localization in the nucleolus (35,36).…”

Evidence that the SKI Antiviral System of Saccharomyces cerevisiae Acts by Blocking Expression of Viral mRNA

“…Ski2p has a glycine-arginine-rich region with homology to several nucleolar proteins (Fig. 3A) such as nucleolin (NSRJ product in S. cerevisiae [11,39,41]), fibrillarin (NOPJ product in S. cerevisiae [30,61]), and the products of GARI (23), SSBJ (36), and NOP3 (58). This type of sequence has also been identified as an RNA-binding motif (37).…”

A comprehensive RRM domains sequence analysis from nucleolin proteins in plants

“…The number of RRMs is similar in nucleolin from yeast, which possess two, compared to animals that contain four RRMs: Four in human (Srivastava et al, 1989); chicken (Maridor and Nigg, 1990); rat (Bourbon and Amalric, 1990); hamster (Lapeyre et al, 1985); mouse (Bourbon et al, 1988); and frog (Rankin et al, 1993); two RRMs in S. cerevisiae (Lee et al, 1992) and S. pombe (Gulli et al, 1995) and two in alfalfa (Bogre et al, 1996), Arabidopsis (Pontvianne et al, 2007) and pea (Tong et al, 1997). Interestingly, within the same nucleolin protein, the RRMs were less conserved in compared with the RRMs from various nucleolin protein.…”