title: Polypeptide formation and polyribosomes in Escherichia coli treated with chloramphenicol.
abstract: In Escherichia coli cultures maximally inhibited with chloramphenicol, formation of polypeptides still continued at a slow, constant rate for at least 90 min. The rate of leucine incorporation was reduced to 0.5%, but methionine was only reduced to 2%, suggesting that chains are normally initiated with methionine but are prematurely released at a short chain length. Consistent with this possibility was the distribution of the products on Sephadex columns: a range of peptides longer than 4 and shorter than 60 to 70 residues was seen. Less than 10% of the peptides broke down during a chase with cold amino acids, and during continuous labeling they accumulated progressively. On the average, one peptide was formed per ribosome every 5 min. Peptide synthesis in the presence of chloramphenicol was still dependent on ribosome translocation; it stopped in a mutant with an inactivated temperature-sensitive elongation factor G. But even in the absence of translocation, new messenger ribonucleic acid (mRNA) chains were found joined to one or a few ribosomes. The chains had a size distribution comparable to that of mRNA from polyribosomes of growing cells. They were stabilized for an average time of about 5 min, but were more rapidly degraded after puromycin was added to the cells. This suggests that stabilization may be related to the average time spent by a ribosome on an mRNA chain, with or without polypeptide formation.
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D001426:Bacterial Proteins / Q000096:biosynthesis*; D002250:Carbon Radioisotopes; D002499:Centrifugation, Density Gradient; D002701:Chloramphenicol / Q000494:pharmacology*; D002845:Chromatography; D004586:Electrophoresis; D004926:Escherichia coli / Q000378:metabolism*; D009693:Nucleic Acid Hybridization; D010452:Peptide Biosynthesis; D011132:Polyribosomes / Q000378:metabolism*; D012329:RNA, Bacterial / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis; D012335:RNA, Ribosomal / Q000096:biosynthesis; D012293:Rifampin / Q000494:pharmacology; D013462:Sulfur Radioisotopes; D013997:Time Factors; D014316:Tritium; D014498:Uracil / Q000378:metabolism; D014529:Uridine / Q000378:metabolism
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D002250:Carbon Radioisotopes; D012329:RNA, Bacterial; D012333:RNA, Messenger; D012335:RNA, Ribosomal; D013462:Sulfur Radioisotopes; D014316:Tritium; D014498:Uracil; D002701:Chloramphenicol; D012293:Rifampin; D014529:Uridine