Control ofPyrimidine Biosynthesis in Pseudomonas aeruginosa

Thepathway ofpyrimidine biosynthesis inPseudomonas aeruginosa hasbeen showntobethesameasinother bacteria. Twenty-seven mutants requiring uracil forgrowth wereisolated andthemutantlesions wereidentified. Mutants lacking either dihydroorotic aciddehydrogenase, orotidine monophosphate pyrophosphorylase, orotidine monophosphate decarboxylase, oraspartic transcarbamylase wereisolated; nonelacking dihydroorotase werefound. Byusing transduction and conjugation, fourgenesaffecting pyrimidine biosynthetic enzymes havebeen identified andshowntobeunlinked toeachother. Thelinkage ofpyrBtomet-28 andilv-2 wasshownbycotransduction. Repression byuracil alone orbybroth could notbedemonstrated foranyenzymes ofthis pathway, incontrast tothe situation inEscherichia coli andSerratia marcescens. Inaddition, derepression of these enzymes could notbedemonstrated. A lowlevel offeedback inhibition of aspartic transcarbamylase wasfound tooccur. Itissuggested thatthecontrol of suchconstitutive biosynthetic enzymes inP.aeruginosa mayberelated tothe comprehensive metabolic activities ofthis organism. Itisknownthatthearrangement ofgenes in bacteria canhaveasignificance forthecontrol of geneproducts. Inparticular, theoperon concept relates thecontiguous arrangement ofstructural genes totheir transcription andcontrol byregulatory genes. Thiscontiguous arrangement isby nomeansuniversal, andbothclustered andunclustered arrangements arefoundinEscherichia coli. Already, 10operons havebeenmapped in E.coli (18), andundoubtedly moreremain tobe identified. Suchanarrangement doesnotseemtobe universal amongbacteria, andvariations onthis themeareimportant toourcomplete understanding ofenzymecontrol mechanisms. The metabolic behavior ofPseudomonas isdifferent inavariety ofwaysfromthatofE.coli. Furthermore,mapping ofPseudomonas hasnotrevealed todateanyevidence ofthegeneclustering necessaryforthetypical operon structure, and, when thesamepathways havebeenmappedinboth bacteria, thegenearrangement inP.aeruginosa hasbeenfound tobequite different. Innocase examined todateisthereclustering ofallthe genes ofanyonepathway. Instead, there appear tobeaggregations oftwoorthree genes, butthese 1Present address: Faculty ofScience, MonashUni