Genetic Separation of Hypoxanthine and Guanine-Xanthine Phosphoribosyltransferase Activities by Deletion Mutations in Salmonella typhimurium

Abstract

Certain proAB deletion mutants of Salmonella typhimurium were found to be simultaneously deleted in a gene required for the utilization of guanine and xanthine (designated gxu). These mutants were resistant to 8-azaguanine and when carrying an additional pur mutation were unable to use guanine or xanthine as a purine source. The defect was correlated with deficiencies in the uptake and phosphoribosyltransferase activities for guanine and xanthine. Hypoxanthine and adenine activities were unaltered. The deficiency was restored to normal by transduction to pro+ and in F' merodiploids.MATERIALS AND METHODS Growth measurements. The minimal salts medium used was medium E described by Vogel and Bonner (29) with glucose (0.2%) as the carbon source.

Mutagenesis of the cyanobacterium Spirulina platensis by UV and nitrosoguanidine treatment

“…Finally, 8-azaguanine-resistant mutants have been identified and characterized in Salmonella typhimurium. The resistance has been linked to mutations of components of the purine biosynthetic pathway such as the nucleoside diphosphokinase (ndk gene), to hypoxanthine and guaninexanthine phosphoribosyltransferase or to the development of permeability barriers [13][14][15][16]. The effect of exposure to UV irradiation on cell viability (Fig.…”

Mutagenic and cytotoxic potencies of a series of anthracycline derivatives as measured by HIS+ reversion, 8‐azaguanine resistance and direct plating cytotoxicity tests in Salmonella typhimurium

“…If not for the recent incorporation of strains TA102 and TA104 into the battery of test strains, only selection for 8-azaguanine resistance would have revealed mutagenic activity associated with N,N-dialkylated anthracycline derivatives. The forward mutation data suggest that structural genes whose modifications confer 8-azaguanine resistance [25,26] may contain DNA squences that-like reversion of hisG428-bearing strainsare compatible with anthracycline mutational mechanisms that vary from those that revert tester strain TA98 to histidine independence. It is also noted that a more quantitative mutation assay measuring resistance to 8-azaguanine and other forward mutation selective screens are presently available [27,28].…”

Transport of nucleic acid bases and nucleosides across the bacterial membrane

“…Group transloca-Bases accumulate predominantly as nucleotide monophosphates in [1,9,21,22] Guanine tion membrane vesicles but not in cells due to rapid post-uptake Xanthine changes; inhibition of uptake by 5'-nucleotides; 3-5-fold stimula-Hypoxanthine tion by PRPP; basal level PRPP-independent uptake results from PRPP pools or a second system and is inhibited by NEM; no stimulation by glucose; distinct phosphoribosyltransferase enzyme for A, H and G-X dissected by mutations; enzymes loosely bound to membrane; loss of enzyme activity results in loss of uptake; K m for adenine uptake, 1.5-2.5 × 10 5 M.…”

“…Distinct PRTase activities for the transport of adenine, hypoxanthine, uracil, nicotinic acid and orotic acid have been identified and in a few instances genetically dissected. The mutational evidence suggests that guanine and xanthine are transported by the same enzymic activity [9]. Hochstadt [1] has speculated, based upon the tendency of PRTases to co-purify and their somewhat overlapping specificity, that they may differ only in specificity towards ligands and not in primary gtructure.…”

“…Some authors have found that there is considerable dissimilarity between inhibitors of transport and PRTase activity [12,13,16]. Experiments with uncouplers and inhibitors of energy metabolism demonstrate that the transport depends upon a protonmotive force [9]. However, inhibitors of energy metabolism will lead to a decrease in the level of PRPP (due to limiting ATP), a co-substrate in conversion of free bases to their respective mononucleotides, thus resulting in an erroneous conclusion regarding direct energy requirement.…”