Two monoclonal antibodies against Escherichia coli ribosomal protein L2 distinguish different locations for their respective epitopes in intact ribosomes

Changes in ribosome function induced by protein kinase associated with ribosomes of Streptomyces collinus producing kirromycin

Protein kinase associated with ribosomes of streptomycetes phosphorylates 11 ribosomal proteins. Phosphorylation activity of protein kinase reaches its maximum at the end of exponential phase of growth. When (32)P-labeled cells from the end of exponential phase of growth were transferred to a fresh medium, after 2 h of cultivation ribosomal proteins lost more than 90% of (32)P and rate of polypeptide synthesis increases twice. Protein kinase cross-reacting with antibody raised against protein kinase C was partially purified from 1 M NH(4)Cl wash of ribosomes and used to phosphorylation of ribosomes. Phosphorylation of 50S subunits (L2, L3, L7, L16, L21, L23, and L27) had no effect on the integrity of subunits but affects association with 30 to 70S monosomes. In vitro system derived from ribosomal subunits was used to examine the activity of phosphorylated 50S at poly(U) translation. Replacement unphosphorylated 50S with 50S possessed of phosphorylated r-proteins leads to the reduction of polypeptide synthesis of about 52%. The binding of N-Ac[(14)C]Phe-tRNA to A-site of phosphorylated ribosomes is not affected but the rate of peptidyl transferase is more than twice lower than that in unphosphorylated ribosomes. These results provide evidence that phosphorylation of ribosomal proteins is involved in mechanisms regulating the translational system of Streptomyces collinus.

Determination of peptide regions exposed at the surface of the bacterial ribosome with antibodies against synthetic peptides

We synthesized six peptides corresponding to regions that are predicted to be surface-exposed of the following ribosomal proteins: protein L2, positions (D263-K272); protein L5, positions (I136-G150); protein L25, positions (Q75-D90); protein S3, positions (Q222-K232) derived from Escherichia coli; and protein L2, positions (K257-K275), and protein S3, positions (R130-T150) from Bacillus stearothermophilus. These peptides were employed to raise ribosomal protein-cross-reactive antibodies. The anti-peptide antisera reacted specifically with their parent proteins, as demonstrated by immunoblotting experiments. In a competition assay proteins L2 from E. coli and B. stearothermophilus as well as proteins L5 and L25 from E. coli were found to be accessible to the respective anti-peptide antibodies in the 50S subunits, but not in 70S ribosomes, proving their location at the 50S interface which is covered by the 30S subunit in the 70S complex. Two of the anti-peptide antisera directed against sequences deduced from protein S3 of E. coli and B. stearothermophilus reacted with 30S subunits as well as with 70S ribosomes, demonstrating their location at the backside, which is exposed to solvent. Thus, by the strategy applied specific short peptide stretches were located at the surface of the ribosome.

Localization of surface peptide from ribosomal protein L7 on 80 S ribosome by biotinylation

A surface topography of ribosomal peptides on ribosome particles was conducted by using N',Hydroxysuccinimido-biotin (NHS-biotin) modification. All rat ribosomal proteins, except proteins L3 and L8, are biotinylated when the ribosome particle is the substrate. A surface peptide from protein L7 was determined from biotinylated ribosomes by high performance liquid chromatography and cyanogen bromide peptide mapping. It was found that only the tandem repeats of the NH2-terminal segment of protein L7 are accessible to biotinylation. It is concluded that the NH2-terminal-end of protein L7 should be exposed on the surface of ribosomal particles.

Interaction of the release factors with the Escherichia coli ribosome: structurally and functionally-important domains

There are two major domains of interaction between the Escherichia coli release factors (RF-1 and RF-2) and each subunit of the ribosome. RF-2 has a binding domain on the shoulder and lower head region of the small subunit at the small lobe distant from the decoding site. This is in close proximity to one of the domains on the large subunit which includes the body dimer of L7/L12 and L11. The other domains of interaction, at the decoding site on the small subunit, and at the peptidyltransferase centre of the large subunit of the ribosome, are some distance from the first two, although the evidence for direct contact with the ribosome is less comprehensive. The release factors may therefore have two distinct structural domains, and in support of this concept RF-1 and RF-2 can both be cleaved into two fragments by papain. Region-specific antibodies, and antibodies against defined peptide within the RF sequences have given an indication that a significant part of an interacting RF molecule is in close proximity to the ribosome surface, confirming an observation by immunoelectron microscopy which suggested that the RF penetrates deeply into the cleft between the two subunits. A region of highly conserved primary sequence between the two release factors from E coli is also conserved in those from B subtilis suggesting it forms an important structural or functional domain. Antibodies against peptides from the N-terminal end of this region strongly inhibit binding of the RF to the ribosome.

Autoantibodies specific for the 20-KDal ribosomal large subunit protein L12

New antibodies reactive with a 20 KDal ribosomal protein of the large subunit were found in sera from two of eighty patients with systemic lupus erythematosus. This antigenic protein was identified as L12 by the mobility in two-dimensional gel electrophoresis. Both sera also contained anti-P activity against three acidic phosphoproteins (P proteins), but this activity was completely inhibited by preincubation with the isolated P proteins. Therefore, these anti-L12 can be useful for studying the function of L12 in protein synthesis.

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.