ABSTRACT
Two types of mutants lacking the second purine nucleoside phosphorylase (PNPase 2) activity were isolated using the Escherichia coli K-12 pndR strains with constitutive or inosine-inducible synthesis of the PNPase 2. The mutations of the first type are recessive to the pndR+ allele on the F' episome. They are closely linked to the original pndR+ mutations and therefore affect the pndR gene encoding the activator protein. The mutations of the second type affect the PNPase 2 structural gene (pndA) and are recessive to the pndA+ allele on the F' episome. The nupC-pndR-pndA-ptsH-cysA gene order was established by means of four- and five-factorial transductional crosses.
Subject(s)
Escherichia coli/genetics , Genes, Bacterial , Genes, Regulator , Genes , Mutation , Pentosyltransferases/genetics , Purine-Nucleoside Phosphorylase/genetics , Chromosome Mapping , Escherichia coli/enzymology , Genetic Markers , Recombination, Genetic , Transduction, GeneticABSTRACT
The synthesis of a second purine nucleoside phosphorylase (PNPII) in the wild type strains of Escherichia coli K-12 is induced by xanthosine. Three types of pndR mutants were studied, which are altered in regulation of PNPII synthesis: 1) constitutive, 2) inducible by nucleosides of hypoxantine and adenine as much as by xanthosine and 3) defective in synthesis of PNPII. All pndR mutations are located in transductional crosses on 51 min of E. coli genetic map. The order of genes established is as follows: pndR-ptsH-cysA. Mutations of the first and second type are dominant, while pndR21 mutation of the third type is recessive to the pndR+ allele on F' episome. The data obtained support the suggestion that the product of pndR regulatory gene is an activator protein necessary for the expression of the PNPII structural gene.
Subject(s)
Chromosome Mapping , Escherichia coli/genetics , Genes, Dominant , Genes, Regulator , Mutation , Pentosyltransferases/genetics , Purine-Nucleoside Phosphorylase/genetics , Alleles , Escherichia coli/enzymology , Genes , Genes, Recessive , Genetics, Microbial , Purine-Nucleoside Phosphorylase/biosynthesis , Transduction, GeneticABSTRACT
Restoration of the ability to catabolise the purine nucleosides in phenotypic revertants of Escherichia coli K-12 mutants defective in deoD encoded purine nucleoside phosphorylase (PNPase 1) is the result of regulatory pndR mutations for synthesis of a second purine nucleoside phosphorylase (PNPase 2). In pndR+ strains synthesis of PNPase 2 is induced by xanthosine; in pndR mutants catabolising all purine nucleosides synthesis of this enzyme is constitutive; in other pndR mutants only catabolising some of purine nucleosides, this catabolisible nucleosides, namely, deoxyinosine, deoxyadenosine as well as, in some cases, inosine and adenosine, act as inducers of PNPase 2 synthesis. In some pndR mutants with inducible PNPase 2, xanthosine is a stronger inducer, in others it is weaker, in comparison with pndR+ strains. In bacterial cells PNPase 2 catalyses the phosphorolytic cleavage of adenosine, inosine, deoxyinosine, guanosine, deoxyguanosine and xanthosine, though in crude extracts adenosine and deoxyadenosine phosphorylase activities of the enzyme are not expressed.