title: Growth and initiation of protein synthesis in Escherichia coli in the presence of trimethoprim.
abstract: Escherichia coli grew exponentially at a reduced rate in the presence of 50 or 100 mug of trimethoprim/ml if the low-molecular-weight products of folate metabolism or their precursors (thymidine, purines, methionine, glycine, and pantothenate) were supplied in the medium. Folate metabolism was inhibited 99.9% by these concentrations of trimethoprim, but a low level of formylation of methionyl transfer ribonucleic acid (met-tRNA(F)) could be detected. However, in a medium containing all major amino acids, nucleosides, and vitamins, formylation of met-tRNA(F) was undetectable in the presence of trimethoprim. No other amino-masked amino acids were detected, and methionine remained a major amino-terminal amino acid of mature proteins. met-tRNA(F) was rapidly labeled with exogenous methionine and was associated with 30s ribosomal subunits and 70s ribosomes. It was concluded that initiation of protein synthesis can occur with unformylated met-tRNA(F) in E. coli. Changes in macromolecular composition were associated with the lack of formylation, in particular a fourfold increase in both met-tRNA(F) and ribosomal subunits. These changes would tend to compensate for the low specific rate of initiation with unformylated met-tRNA(F).
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000096:biosynthesis*; D003470:Culture Media; D004926:Escherichia coli / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D005493:Folic Acid Antagonists / Q000494:pharmacology*; D005561:Formates / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D010442:Peptide Chain Initiation, Translational; D011132:Polyribosomes / Q000378:metabolism; D011687:Purines / Q000096:biosynthesis; D011743:Pyrimidines / Q000494:pharmacology*; D012329:RNA, Bacterial / Q000378:metabolism; D012343:RNA, Transfer / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D013053:Spectrophotometry; D013941:Thymine / Q000096:biosynthesis; D014295:Trimethoprim / Q000494:pharmacology; D014316:Tritium
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D003470:Culture Media; D005493:Folic Acid Antagonists; D005561:Formates; D011687:Purines; D011743:Pyrimidines; D012329:RNA, Bacterial; D014316:Tritium; D012694:Serine; D012343:RNA, Transfer; D008715:Methionine; D014295:Trimethoprim; D013941:Thymine