Peptide analyses of a protein component, 50-8, of 50s ribosomal subunit from erythromycin resistant mutants of Escherichia coli and Escherichia freudii

Peptide analysis of RNA polymerase alpha subunit from Escherichia coli: comparison of free with assembled form

The analysis of tryptic peptides was performed on the unassembled as well as assembled form f alpha subunit of the DNA-dependent RNA polymerase from Escherichia coli. The peptide profiles obtained by Dowex 50 column chromatography of the unassembled alpha subunit prepared from cells, either pulse-labeled or continuously labeled with radioactive lysine or arginine, were essentially identical with those of the alpha subunit from intact RNA polymerase. The results suggest that newly synthesized free alpha subunit is assembled into the polymerase structure without any remarkable modifications. The number of lysine- and arginine-containing peaks were close to the values expected from the amino acid composition of alpha subunit assuming that the two alpha subunits in RNA polymerase core enzyme have identical primary structure.

Localization of five antibiotic resistances at the subunit level in chloroplast ribosomes of Chlamydomonas

The chloroplast ribosomes from five antibiotic resistant strains of Chlamydomonas, each carrying one mutant gene mapping in chloroplast DNA, have been shown to be resistant to the corresponding antibiotic in a poly(U)-directed amino-acid incorporating assay system. The alteration conferring resistance was localized to the 30S subunit in ribosomes from streptomycin, neamine, and spectinomycin resistant strains, and to the 50S subunit in ribosomes from cleocin and carbomycin resistant strains. Spectinomycin resistant ribosomes showed no cross-resistance to any other drugs, but limited cross-resistance was noted with the other mutant ribosomes. The similarity between these findings and results reported by others with bacterial ribosomes supports our hypothesis that at least some chloroplast ribosomal proteins are coded by genes in chloroplast DNA.

Mutation to erythromycin dependence in Escherichia coli K-12

A nitrosoguanidine-induced mutant of Escherichia coli K-12 strain JC12 was absolutely dependent on erythromycin or related macrolide antibiotics for growth. The only other drugs which permitted growth (lincomycin and chloramphenicol) are, like the macrolides, inhibitors of the 50S ribosome. The order of relative effectiveness of these drugs was macrolides > lincomycin > chloramphenicol. Rates of growth with all drugs were concentration dependent. Erythromycin starvation was followed by normal rates of increase in cell mass and macromolecular synthesis for approximately one mass-doubling time, after which macromolecular synthesis abruptly ceased and cell lysis and death occurred. The dependent mutant gave rise spontaneously to revertants to independence with very high frequency (10(-4)). The gene (mac) for macrolide dependence is located near minute 25 on the E. coli chromosome; it does not result in increased resistance to these drugs. A separate gene for erythromycin resistance (eryA) is located in the cluster of ribosomal structural genes near spc, close to minute 63. Dependence on macrolides was most clearly evident in strains carrying mutations at both eryA and mac.

Altered chlorplast ribosomal proteins associated with erythromycin-resistant mutants in two genetic systems of Chlamydomonas reinhardi

The phenotype of several erythromycin-resistant mutants of Chlamydomonas reinhardi was further characterized in terms of the electrophoretic properties of their chloroplast ribosomal proteins. In mutant ery-M2d a single protein of the large (52 S) subunit has altered properties, which probably result from a change in its primary sequence. This mutation is inherited in a Meudelian manner. In mutant ery-U1a, which is inherited in a uniparental manner, a different single protein of the 52 S subunit is altered. This change might result from a change in either the primary sequence of the protein or in some form of secondary modification. These results indicate that these two distinct genetic systems must cooperate in the production of chloroplast ribosomes.