The gua Operon of Escherichia coli K-12: Evidence for Polarity from guaB to guaA
AUTOR(ES)
Lambden, Paul R.
RESUMO
Guanine auxotrophs of Escherichia coli K-12 were isolated after mutagenesis with N-methyl-N′-nitro-N-nitrosoguanidine, ethyl methane sulfonate, or the acridine mustard ICR 372. guaA (xanthosine 5′-monophosphate [XMP] aminase-less) mutants were distinguished from guaB (inosine 5′-monophosphate [IMP] dehydrogenase-less) mutants by their growth response to xanthine and by enzyme assay. Mutations were classified as base substitutions or frameshift on the basis of mutagen-induced reversion patterns. All guaA strains, including three frameshift mutants, produced derepressed levels of IMP dehydrogenase when cultured with a growth-limiting concentration of guanine. The guaB strains were of two types: (i) those producing derepressed levels of XMP aminase, and (ii) those producing basal levels of XMP aminase when grown under conditions of guanine starvation. In the guaB strains of the second type, the expression of the adjacent guaA gene is reduced. It is proposed that this pleiotropic effect of some guaB mutations is a result of polarity. The orientation of polarity suggests the gene order “operator”-guaB-guaA. Gel diffusion studies with IMP dehydrogenase antiserum showed that strains carrying polar guaB mutations do not produce cross-reacting material (CRM). The remaining guaB mutants were either CRM+ or CRM−. Mapping the mutations by three-factor crosses showed that polar and nonpolar guaB sites are clustered in a small genetic region cotransducible with guaA. The relative positions of the guaB mutational sites established that the polar mutations lie within the structural gene for IMP dehydrogenase.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=246347Documentos Relacionados
- Nucleotide sequence of the guaB locus encoding IMP dehydrogenase of Escherichia coli K12.
- In Vivo and In Vitro Complementation Between guaB and In Vivo Complementation Between guaA Auxotrophs of Salmonella typhimurium
- Secondary attachment site for bacteriophage lambda in the guaB gene of Escherichia coli.
- Threonine Locus of Escherichia coli K-12: Genetic Structure and Evidence for an Operon
- Orientation of the guanine operon of Escherichia coli K-12 by utilizing strains containing guaB-xse and guaB-upp deletions.