Binding of rat ribosomal proteins to yeast 5.8S ribosomal ribonucleic acid

Ribosomal protein L35 is required for 27SB pre-rRNA processing in Saccharomyces cerevisiae

Ribosome synthesis involves the concomitance of pre-rRNA processing and ribosomal protein assembly. In eukaryotes, this is a complex process that requires the participation of specific sequences and structures within the pre-rRNAs, at least 200 trans-acting factors and the ribosomal proteins. There is little information on the function of individual 60S ribosomal proteins in ribosome synthesis. Herein, we have analysed the contribution of ribosomal protein L35 in ribosome biogenesis. In vivo depletion of L35 results in a deficit in 60S ribosomal subunits and the appearance of half-mer polysomes. Pulse-chase, northern hybridization and primer extension analyses show that processing of the 27SB to 7S pre-rRNAs is strongly delayed upon L35 depletion. Most likely as a consequence of this, release of pre-60S ribosomal particles from the nucleolus to the nucleoplasm is also blocked. Deletion of RPL35A leads to similar although less pronounced phenotypes. Moreover, we show that L35 assembles in the nucleolus and binds to early pre-60S ribosomal particles. Finally, flow cytometry analysis indicated that L35-depleted cells mildly delay the G1 phase of the cell cycle. We conclude that L35 assembly is a prerequisite for the efficient cleavage of the internal transcribed spacer 2 at site C(2).

Abnormalities of the large ribosomal subunit protein, Rpl35a, in Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is an inherited bone marrow failure syndrome characterized by anemia, congenital abnormalities, and cancer predisposition. Small ribosomal subunit genes RPS19, RPS24, and RPS17 are mutated in approximately one-third of patients. We used a candidate gene strategy combining high-resolution genomic mapping and gene expression microarray in the analysis of 2 DBA patients with chromosome 3q deletions to identify RPL35A as a potential DBA gene. Sequence analysis of a cohort of DBA probands confirmed involvement RPL35A in DBA. shRNA inhibition shows that Rpl35a is essential for maturation of 28S and 5.8S rRNAs, 60S subunit biogenesis, normal proliferation, and cell survival. Analysis of pre-rRNA processing in primary DBA lymphoblastoid cell lines demonstrated similar alterations of large ribosomal subunit rRNA in both RPL35A-mutated and some RPL35A wild-type patients, suggesting additional large ribosomal subunit gene defects are likely present in some cases of DBA. These data demonstrate that alterations of large ribosomal subunit proteins cause DBA and support the hypothesis that DBA is primarily the result of altered ribosomal function. The results also establish that haploinsufficiency of large ribosomal subunit proteins contributes to bone marrow failure and potentially cancer predisposition.

Inhibition of cell death by ribosomal protein L35a

In order to better understand how tumor cells develop resistance to chemotherapy drugs, we screened a human cDNA expression library in Jurkat cells for cDNA's that conferred resistance to doxorubicin-induced cell death. One of the cDNA's isolated in the screen codes for ribosomal protein L35a, a component of the large subunit of the ribosome. Jurkat cells engineered to overexpress L35a protein were more resistant not only to doxorubicin but also to UV-irradiation, anti-Fas antibody, and serum starvation compared to Jurkat cells expressing endogenous levels of L35a. Jurkat cells overexpressing L35a did not have increased levels of the anti-apoptotic proteins Bcl-2 or Bcl-xL, the drug efflux pump P-glycoprotein, nor altered cellular growth kinetics or total protein synthesis. Our results provide new insight into L35a function and suggest that it may have a role in the cellular response to cytotoxic damage. Since L35a RNA is overexpressed in a significant number of glioblastoma multiforme (GBM) brain tumors, our results may stimulate further investigation into the possible role of L35a in the resistance of GBM to cytotoxic therapy.

Yeast ribosomal proteins L4, L17, L20, and L25 exhibit different binding characteristics for the yeast 35S precursor rRNA

In vitro synthesized radioactive yeast 35S precursor rRNA (35S pre-rRNA) molecules were used to determine the binding characteristics of 13 proteins from the yeast 60S ribosome subunit. L4, L17, L20 and L25 were found to bind the 35S pre-rRNA molecule in vitro in the absence of any other cellular components as determined by a modified membrane filtration assay and an agarose gel mobility shift assay. In all cases, RNA-protein complex formation was proportional to the amount of protein added to the binding reaction mixture. Binding to the pre-rRNA could be saturated yielding a molar RNA/protein ratio approaching one. Non-radioactive 35S pre-rRNA transcript competed for the binding in a dosage-dependent manner. Presence of 18S rRNA species and poly(A) did not affect their binding to the 35S RNA. However, in the presence of the 25S rRNA species, the four proteins exhibited distinct binding characteristics for the pre-rRNA molecule. L4 did not bind the 25S rRNA but interacted specifically with the 35S pre-rRNA molecule with a binding constant of 4.4x10(6)/M. L17 bound the pre-rRNA molecule preferentially (Ka=17x10(6)/M) but also bound the mature 25S rRNA species (Ka=10x10(6)/M). L20 bound both the pre-rRNA molecule and the 25S rRNA species equally well (Ka=11-12x10(6)/M). L25 also bound both the 35S pre-rRNA and the mature 25S rRNA with slightly different affinities, with Ka=3.1 vs. 2.5x10(6)M, respectively. We speculate that L4, L17, and L25 are among the early assembled ribosomal proteins but L4 may be one of the first ribosomal proteins that bind to the 35S pre-rRNA molecule during ribosome biogenesis.

Isolation of a mouse DNA fragment with homology to a Drosophila ribosomal protein gene

A mouse genomic library in lambda Charon 4A was screened for putative ribosomal protein genes using a fragment of the gene encoding Drosophila ribosomal protein 49 as a hybridization probe under nonstringent hybridization conditions. A recombinant phage was selected and its restriction enzyme map determined. The major species of mouse poly(A)+ mRNA homologous to the putative gene is about 740 nucleotides long.

Acrylamide gel analysis of sucrose gradient-derived RNA B fractions transferring delayed sensitivity in vitro

Sucrose-derived RNA fractions transferring specific delayed sensitivity in vitro were extracted from mono-(p-azobenzenearsonate)-N-chloracetyl-L-tyrosine (ARSNAT)- or keyhole limpet hemocyanin (KLH)-sensitized guinea pigs. Fractions having biological activity were assessed by acrylamide gel analysis to enumerate the number of RNA species in active fractions, and to compare and examine the banding patterns of each RNA fraction. Each isolated B fraction of RNA exhibited multiple bands of RNA with molecular weights ranging from 4.0 X 10(5) to 8.5 X 10(5). Depending on the source and antigen sensitivity of the RNA donor, several differences were observed among the analyzed fractions. These were bands of varying intensity, presence of additional RNA bands, absence of bands in certain positions, and RNA bands migrating in different positions on the gels. Acrylamide gel analysis separation, and resolution of B fractions with specific immunobiological activity now offers an approach for further isolation and resolution of the active species.