Gramicidin SBiosynthesis OperonContaining theStructural Genes grsAandgrsBHasan OpenReading FrameEncoding a Protein Homologous toFatty AcidThioesterases

TheDNA sequenceofabout5.9kilobase pairs (kbp)ofthegramicidin S biosynthesis operon (grs) was determined. Three openreading frames wereidentified; thecorresponding genes,cafledgrsT, grsA,andgrsB, were foundtobeorganized inone transcriptional unit, nottwoas previously reported (M.Krauseand M.A.Marahiel, J.Bacteriol. 170:46694674, 1988). Theentire nucleotide sequenceofgrsA, coding forthe 126.663-kilodalton gramicidin Ssynthetase 1,grsT, encoding a29.191-kilodalton protein ofunknown function, and732bpofthe5'endofgrsB, encoding thegramicidin Ssynthetase 2,weredetermind. Adngle initiation site oftranscription 81bpupstreamofthegrsTinitiation codonGTG was identified byhigh-resolution S1 mapping studies. Thesequenceofthe grsA geneproduct showed a high degree ofhomoogytothetyrocidine synthetase 1(TycAprotein), andthat ofgrsTexhibited asignUicant degree ofhomology tovertebrate fatty acid thioesterases. Inresponse tocertain nutrient conditions usually associatedwithnutrient depletion, gram-positive bacteria ofthe genus Bacillus induce theprocess ofendospore formation as wellastheproduction ofsecondary metabolites suchas peptide antibiotics andextracellular proteases (4,26,41). In bothcases, genesareactivated atthetransition fromlogarithmic tostationary phaseofgrowth. Expression ofthese genesdepends ontheproducts ofspoOloci (10, 26,30,41). Tounderstand thecomplex relationship between induction ofsporulation'and production ofsecondary metabolites, we andothers haveisolated andstudied theorganization and regulation ofsomeantibiotic biosynthesis genes atthemolecular level. Genesencoding multifunctional enzymes involved inbiosynthesis ofthecyclic antibiotics bacitracin, gramicidin S,andtyrocidine havebeenidentified (16, 20, 33). Thenonribosomal synthesis ofthese antibiotics bythe so-called protein-thiotemplate mechanism hasbeenstudied