Complexes containing rat liver 80s ribosomes treated with puromycin and high concentrations of KCl, elongation factor 2 (EF-2) from pig liver, and guanosine 5'-[/3,y-methylene]triphosphate were prepared. Neighboring proteins in the complexes were cross-linked with the bifunctional reagent 2-iminothiolane. Proteins were extracted and then separated into 22 fractions by chromatography on carboxymethylcellulose of which seven fractions were used for further analyses. Each protein fraction was subjected to diagonal polyacrylamide/sodium dodecyl sulfate gel electrophoresis. Nine cross-linked protein pairs between EF-2 and ribosomal proteins were shifted from the line formed with monomeric proteins. The spots of ribosomal proteins cross-linked to EF-2 were cut out from the gel plate and labelled with lZ5I. The labelled protein was extracted from the gel and identified by three kinds of two-dimensional gel electrophoresis, followed by autoradiography. The following proteins of both large and small subunits were identified: L9, L12, L23, LA33 (acidic protein of M, 33000), P2, S6 and S23/ S24, and L3 and L4 in lower yields. The results are discussed in relation to the topographies of ribosomal proteins in large and small subunits. Furthermore we found new neighboring protein pairs in large subunits, LA33 -L11 and LA33 -L12.During protein biosynthesis in eukaryotic cells, elongation factor 2 (EF-2) interacts with ribosomes in the presence of GTP and catalyzes the translocation of newly synthesized peptidyl-tRNA from the aminoacyl-tRNA binding site (the A site) of ribosomes to the peptidyl-tRNA site (the P site) [l -31. The functional roles of ribosomal proteins in the translocation are as yet unknown. To understand the molecular mechanisms of the translocation in mammalian ribosomes, it is important to identify proteins in the EF-2 binding site of ribosomes.Employing four kinds of cross-linking reagents and hydrogen peroxide, we identified 62 cross-linked protein pairs involving 36 protein species containing two acidic proteins of rat liver 60s subunits and have discussed these in relation to other functional data [4, 51. Concerning the 40s subunits, similar data were presented by Tolan and Traut [6]. Therefore, it is of interest that ribosomal proteins which interact with elongation factors have been determined.In the present experiments we investigated EF-2-binding sites in rat liver 80s ribosomes, employing 2-iminothiolane. Cross-linked proteins were analyzed by a modified method of diagonal SDS gel electrophoresis [7]. Seven large-subunit proteins and two small-subunit proteins were identified as the components cross-linked to EF-2. The mutual locations of these proteins in the 80s ribosomes are discussed.

No abstract

Rat liver 40S ribosomal subunits were treated with a bifunctional imidoester, dimethyl 3,3'-dithiobispropionimidate (DTP), and the neighboring protein pairs were identified. The cross-linked proteins were analyzed by acrylamide/SDS diagonal gel electrophoresis (Sommer & Traut (1974) Proc. Natl. Acad. Sci. U.S. 71, 3946-3950). The cross-linked components that fell off the diagonal upon adding 2-mercaptoethanol in the second dimension were labeled with 125I in the acrylamide gel and identified by two-dimensional acrylamide/urea gel electrophoresis, followed by radioautography. Considering these results and the molecular weights, we propose the following ten pairs, according to our numbering system (Terao & Ogata (1975) Biochim. Biophys. Acta 402, 219-229): S3-S5 (S3/S3a-S4), S3-S14 (S3/S3a-S14), S3-S17 (S3/S3a-S16), S5-S22 (S4-S23/S24), S10-S12 (S8-S11), S9-S16 (S9-S18), S9-S22 (S9-S23/S24), S6-S23 (S5-S25), S17-S21 (S16-S19), and S16-S26 (S18-S27). The designation according to the proposed uniform nomenclature (McConkey et al. (1979) Mol. Gen. Genet. 169, 1-6) are given in parentheses.

(1) When rat liver 40 S ribosomal proteins in 6 M urea were were mixed with poly(U) at an appropriate ratio, a precipitate was formed which was also insoluble in the sample solution for two-dimensional acrylamide gel electrophoresis. Analyses by two-dimensional acrylamide gel electrophoresis showed that S7 and S10 proteins (according to our numbering system) had disappeared selectively from the fraction soluble in 6 M urea. These two proteins were present in the fraction insoluble in 6 M urea, and became soluble in the sample solution after treating it with RNase. The results suggest that S7 and S10 proteins have strong affinities for poly(U). When rat liver 40 S subunits were incubated with poly(U), similar results were obtained. (2) After incubation of 40 S subunits with [3H]poly(U) and then with unlabeled poly(U), UV irradiation cross-linked poly(U) to the protein moiety of the 40 S subunit. When the protein fraction insoluble in the sample solution for two-dimensional electrophoresis was prepared from 40 S subunits cross-linked to poly(U) and then subjected to two-dimensional acrylamide gel electrophoresis after RNase treatment, S7 and S10 proteins were detected on the gel. In addition to the S7 protein spot, a triangular area spreading from the spot to the origin contained radioactivity. The results suggest that poly(U) is cross-linked to S7 protein and oligo(U) fragments bound to S7 protein affect its electrophoretic mobility. (3) Ribosomal proteins were prepared from 40 S subunits cross-linked to carrier-free [3H]poly(U) and analyzed by three-dimensional acrylamide gel electrophoresis (Terao, K. & Ogata, K. (1975) Biochim. Biophys. Acta 402, 214--229) after RNase treatment. It was found that S7, S6, and S15 proteins are cross-linked to poly(U). From the results of the present and preceding experiments it is concluded that S7 is the poly(U)-binding protein. The possibility that other proteins in 40 S ribosomal subunits interact with poly(U) is discussed.

No abstract