Three-dimensional location of ribosomal protein BL2 from Bacillus stearothermophilus, a key component of the peptidyl transferase center

Immunoelectron microscopic localization of ribosomal proteins BS8, BS9, BS20, BL3 and BL21 on the surface of 30S and 50S subunits from Bacillus stearothermophilus

The locations of ribosomal proteins BS8, BS9 and BS20 on the 30S subunit of Bacillus stearothermophilus ribosomes, and of BL3 and BL21 on the 50S subunit, were determined by immunoelectron microscopy. BL3 was found to lie half-way down the body of the 50S subunit on the interface side, below the L7/L12 stalk, in agreement with the placement of the corresponding protein in Escherichia coli by neutron-scattering; BL21 was located at a similar position on the solvent side of the subunit, as predicted by cross-linking experiments with E. coli ribosomes. Similarly, BS8 was found in the upper region of the body of the 30S subunit on the solvent side, and BS9 on the top of the head of the subunit, also on the solvent side, both positions being in good agreement with neutron-scattering data and other immunoelectron microscopy results. In contrast, BS20 was found to lie at the extreme base of the body of the 30S subunit; this placement is not compatible with the location of E. coli S20 by neutron-scattering but fits very plausibly with other biochemical data, such as sites of RNA-protein footprinting on 16S RNA, relating to the location of S20 in E. coli.

Nuclear-encoded chloroplast ribosomal protein L27 of Nicotiana tabacum: cDNA sequence and analysis of mRNA and genes

A tobacco (Nicotiana tabacum cv. Petite Havana) leaf cDNA library was constructed in the expression vector lambda gt11. Immunological and nucleic acid hybridization screening yielded several cDNAs encoding an M(r) 19,641 precursor to an M(r) 14,420 mature protein which is homologous to Escherichia coli ribosomal protein L27. One cDNA (L27-1; 882 nucleotides long) contains 104 bp of 5'-noncoding sequence, 51 codons for a transit peptide, 128 codons for the predicted mature L27 polypeptide, and 241 bp of 3'-noncoding sequence, including the poly(A)29 tail. A beta-galactosidase-L27 fusion protein was bound to nitrocellulose filters, expressed, and used as an affinity matrix to purify monospecific antibody to L27 protein from an antiserum of rabbits immunized with 50S chloroplast ribosomal proteins. Using this monospecific antibody, protein L27 was identified among HPLC-purified tobacco chloroplast ribosome 50S subunit proteins. The predicted amino terminus of the mature L27 protein was confirmed by partial sequencing of the HPLC-purified L27 protein. The mature L27 protein has 66%, 61%, 56%, and 48% amino acid sequence identity with the L27-type ribosomal proteins of Bacillus subtilis, E. coli, Bacillus stearo-thermophilus, and yeast mitochondria (MRP7), respectively, in the homologous overlapping regions. The transit peptide of tobacco chloroplast ribosomal protein L27 has 41% amino acid sequence similarity with the MRP7 mitochondrial targeting sequence. Tobacco chloroplast L27 protein also has a 40 amino acid long carboxyl-terminal extension (compared to its bacterial counterparts) which is similar to the corresponding portion of yeast MRP7.(ABSTRACT TRUNCATED AT 250 WORDS)

A consonant model of the tRNA-ribosome complex during the elongation cycle of translation

Chemical and photochemical affinity techniques have been used extensively to determine the positions of the tRNA binding sites on the Escherichia coli ribosome. Recent advances in our understanding of ribosome structure and function prompted us to critically review the data that have accumulated on tRNA-ribosome cross-links. As a result, we propose a new model of the tRNA-ribosome complex that accounts for nearly all of the pertinent evidence.

The complex between ribosomal proteins and aminoacyl-tRNA: the interactions and hydrolytic activities are not confined to the proteins L2 and L16 of Escherichia coli ribosomes

The capacity of some Escherichia coli (E. coli) ribosomal proteins to bind to tRNA and to hydrolyse their aminoacylated derivatives has been analysed. The following results were obtained: (1) The basic proteins L2, L16 and L33 and S20 bound f[3H]Met-tRNA to a similar extent as the total proteins from 30 S (TP30) or 50 S (TP50) when tested by nitrocellulose filtration, in contrast to the more acidic proteins L7/L12 and S8. (2) The proteins of the peptidyltransferase centre, L2 and L16, showed no distinct specificity, binding various charged tRNAs from E. coli and Saccharomyces cerevisiae (S. cerevisiae). (3) A number of isolated ribosomal proteins hydrolysed aminoacyl-tRNA as assessed by trichloroacetic acid precipitation, in contrast to the TP30 and TP50. (4) The loss of radiolabel from Ac[14C]Phe-tRNA and from [14C]tRNA in the presence of these proteins could not be prevented by RNasin, a ribonuclease inhibitor, whereas that mediated by a sample of non-RNase-free bovine serum albumin was inhibited. (5) When double-labelled, Ac[3H]Phe-[14C]tRNA was incubated with L2 both radiolabels were lost, indicating that this potential candidate for a peptidyltransferase enzyme does not specifically cleave the ester bond between the aminoacyl residue and the tRNA.

Labeling the peptidyltransferase center of the Escherichia coli ribosome with photoreactive tRNA(Phe) derivatives containing azidoadenosine at the 3' end of the acceptor arm: a model of the tRNA-ribosome complex

Photoreactive derivatives of yeast tRNA(Phe) containing 2-azidoadenosine (2N3A) at position 73 or 76 have been crosslinked to the peptidyl site of Escherichia coli ribosomes. Covalent tRNA-ribosome attachment was dependent upon the replacement of adenosine by 2N3A in the tRNA, irradiation with 300-nm light, and the presence of poly(U). In all cases, the modified tRNAs became crosslinked exclusively to 50S ribosomal subunits. While the tRNA derivative containing 2N3A at position 73 labeled only protein L27, that containing 2N3A at position 76 labeled proteins L15, L16, and L27 as well as a segment of the 23S rRNA. The site of crosslinking in the rRNA was identified as guanosine-1945, which lies within a highly conserved sequence adjacent to a number of modified bases and has not until now been identified at the peptidyltransferase center. On the basis of these results, and previously reported crosslinks from tRNA containing 8-azidoadenosine in the 3'-terminal -A-C-C-A sequence [Wower, J., Hixson, S. S. & Zimmermann, R. A. (1988) Biochemistry 27, 8114-8121], we propose a model for the arrangement of tRNA molecules at the peptidyl and aminoacyl sites that is consistent with most of the information available about the location of the peptidyltransferase center and the decoding domain of the E. coli ribosome.

Immunoblotting analysis of protein-protein crosslinks within the 50S ribosomal subunit of Escherichia coli. A study using dimethylsuberimidate as crosslinking reagent

50S ribosomal subunits of Escherichia coli have been crosslinked with the bifunctional imidoester dimethyl-suberimidate and the protein-protein crosslinks have been analyzed by immunoblotting, using antisera specific for the individual ribosomal proteins of the large ribosomal subunit. Crosslinked protein pairs which occurred in yields higher than 5% have been unambiguously identified. Thus 13 crosslinks have been identified, namely L1-L33, L5-L7/12, L6-L19, L7/12-L10, L7/12-L11, L9-L28, L10-L11, L13-L20, L16-L27, L17-L32, L18-L22, L19-L25 and L27-L33. These data, together with the results which we will be presenting elsewhere, contribute considerably to our knowledge of the protein topography of the 50S ribosomal proteins as determined by immunoelectron microscopy. We can now propose the approximate locations of ten proteins that have not previously been localized.

Localization of proteins L4, L5, L20 and L25 on the ribosomal surface by immuno-electron microscopy

Ribosomal proteins L4, L5, L20 and L25 have been localized on the surface of the 50S ribosomal subunit of Escherichia coli by immuno-electron microscopy. The two 5S RNA binding proteins L5 and L25 were both located at the central protuberance extending towards its base, at the interface side of the 50S particle. L5 was localized on the side of the central protuberance that faces the L1 protuberance, whereas L25 was localized on the side that faces the L7/L12 stalk. Proteins L4 and L20 were both located at the back of the 50S subunit; L4 was located in the vicinity of proteins L23 and L29, and protein L20 was localized between proteins L17 and L10 and is thus located below the origin of the L7/L12 stalk.