Stability and homogeneity of preparations of ribosomal particles from Escherichia coli

Photo-induced affinity labeling of Escherichia coli ribosomes by chloramphenicol

In order to obtain more information about the binding site for chloramphenicol (D-threo diastereoisomer) on the bacterial ribosome, photo-affinity labeling experiments of this receptor have been performed with [3H]chloramphenicol itself. Control experiments show that this drug can be split photochemically by ultraviolet irradiation, whereas the ribosome is not modified structurally or functionally by such a treatment. When photolysis of a mixture of chloramphenicol and ribosomes is performed under critical conditions, some proteins like L1, L11, S3 and S4 are radiolabeled. L11, S3 and S4 are radiolabeled specifically as demonstrated by photo-incorporation experiments with isotopically diluted [3H]chloramphenicol or by comparison of the results obtained here with reversible experiments performed by the isotopic dilution method. When the D-erythro diastereoisomer of chloramphenicol is photo-incorporated into the bacterial ribosome, proteins are radiolabeled only in a non-specific way. These results show that this material could be used as an efficient scavenger. When finally D-threo [3H]chloramphenicol is photo-incorporated in the presence of a large amount of the D-erythro diastereoisomer, the radiolabeling pattern obtained for the proteins is quite different from that expected: while L11 is still labeled fairly extensively, L27 is the most radiolabeled protein found.

[Purification of the bacterial ribosome using chloramphenicol and erythromycin columns]

Chloramphenicol and erythromycin are antibiotics whose target is the bacterial ribosome. We have studied the possibility of isolating the bacterial ribosome by affinity chromatography on chloramphenicol and erythromycin columns. Several columns have been prepared using different spacers and methods of attachment of the ligands (cyanogen bromide, bis-expoxyde). The efficiency and specificity of these columns is discussed. Ethylene diamine is not always suitable as a spacer, because it presents non specific affinity for the ribosome. Pure tight ribosomes have been prepared by ultracentrifugation. They have been compared to ribosomes from affinity columns. These columns have no denaturing effect on ribosomes. They allow a good purification of ribosomes starting from crude bacterial extracts, but the separation of tight couples from loose subunits is not possible.

X-ray and neutron small-angle scattering studies of the complex between protein S1 and the 30-S ribosomal subunit

X-ray neutron solution scattering experiments have been done to investigate the influence of the binding of ribosomal protein S1 on the conformation of the 30-S ribosomal subunit of Escherichia coli. The following conclusions were made. 1. The alterations (if any) in conformation of the non-S1 parts of the 30-S subunit induced by S1 binding are too small to be detected (less than 0.1 nm change in radius of gyration). 2. The center of gravity of protein S1 bound to the 30-S subunit is quite far from the center of gravity of the particle (approximately 7.5 nm).

Release of certain ribosomal proteins from 70-S Escherichia coli ribosomes by mild ribonuclease digestion

A method for the release of some proteins from Escherichia coli (MRE 600)ribosomes is described, avoiding extraction with denaturing reagents. High-salt-washed, 70-S ribosomes were treated with pancreatic ribonuclease which led to the release of 12 proteins of the larger ribosomal subunit. Separation of released protein was first attempted by gel filtration and by fractionation with (NH4)2SO4. The number and type of the released proteins were identified by sodium dodecyl sulphate-polyacrylamide gels and two-dimensional gel electrophoresis. The method should prove of use in the large scale purification of proteins L1, L7, and L25.

Ribosomal protein S1 and polypeptide chain initiation in bacteria

Among several subspecies of 30S subunits of Escherichia coli observed by polyacrylamide-agarose gel electrophoresis, only the slow-moving, protein S1-containing subspecies participates in the formation of the 30S initiation complex with coliphage MS2 RNA as mRNA; the other subspecies retain activity with AUG as mRNA; they are also active in the poly(U)-directed binding of Phe-tRNA. Protein S1 from Caulobacter crescentus substitutes for E. coli S1 despite the fact that C. crescentus ribosomes do not bind MS2 RNA. Under appropriate conditions, the entire population of E. coli 30S subunits can be isolated as the S1-containing subspecies. Protein S1 is lost by salt treatment of ribosomes.