title: Regulation of the tyrosine biosynthetic enzymes in Salmonella typhimurium: analysis of the involvement of tyrosyl-transfer ribonucleic acid and tyrosyl-transfer ribonucleic acid synthetase.
abstract: Mutants of Salmonella typhimurium were isolated that require tyrosine for growth because of an altered tyrosyl-transfer ribonucleic acid (tRNA) synthetase. Extracts of one strain (JK10) contain a labile enzyme with decreased ability to transfer tyrosine to tRNA(Tyr) and a higher K(m) for tyrosine than the wild-type enzyme. Strain JK10 maintains repressed levels of the tyrosine biosynthetic enzymes when the growth rate is restricted due to limitation of charged tRNA(Tyr). Several second-site revertants of strain JK10 exhibit temperature-sensitive growth due to partially repaired, heat-labile tyrosyl-tRNA synthetase. The tyrosine biosynthetic enzymes are not derepressed in thermosensitive strains grown at the restrictive temperature. A class of tyrosine regulatory mutants, designated tyrR, contains normal levels of tyrosyl-tRNA synthetase and tRNA(Tyr). These results suggest that charging of tRNA(Tyr) is not necessary for repression. This conclusion is substantiated by the finding that 4-aminophenylalanine, a tyrosine analogue which causes repression of the tyrosine biosynthetic enzymes, is not attached to tRNA(Tyr) in vivo, nor does it inhibit the attachment reaction in vitro. A combined regulatory effect due to the simultaneous presence of tyrS and tyrR mutations in the same strain was detected. The possibility of direct participation of tyrosyl-tRNA synthetase in tyrosine regulation is discussed.
mesh_terms: D000446:Aldehyde-Lyases / Q000378:metabolism; D000596:Amino Acids / Q000494:pharmacology; D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D002474:Cell-Free System; D003510:Cyclohexanes; D004794:Enzyme Repression; D005809:Genes, Regulator; D006836:Hydro-Lyases / Q000378:metabolism; D007930:Leucine / Q000378:metabolism; D009154:Mutation; D009574:Nitro Compounds / Q000494:pharmacology; D010088:Oxidoreductases / Q000378:metabolism; D010649:Phenylalanine / Q000494:pharmacology; D011773:Pyruvates; D012343:RNA, Transfer / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000201:enzymology* / Q000254:growth & development / Q000378:metabolism; D014161:Transduction, Genetic; D014316:Tritium; D014443:Tyrosine / Q000096:biosynthesis* / Q000378:metabolism / Q000494:pharmacology; D014444:Tyrosine Transaminase / Q000378:metabolism
chemical_list: D000596:Amino Acids; D003510:Cyclohexanes; D009574:Nitro Compounds; D011773:Pyruvates; D014316:Tritium; D014443:Tyrosine; D010649:Phenylalanine; D012343:RNA, Transfer; D010088:Oxidoreductases; D014444:Tyrosine Transaminase; D000446:Aldehyde-Lyases; D006836:Hydro-Lyases; D000604:Amino Acyl-tRNA Synthetases; D007930:Leucine