Magnesium transport in XXXX : characterization of magnesium influx and cloning of a transport gene.

@entity2491 @entity1025 @entity3281 @entity515 @entity2400 @entity8926 @entity2624
The influx of @entity1025 in @entity8926 was studied by both kinetic and genetic techniques. Wild-type cells grown in a high @entity2400 concentration (10 mM) exhibited a Km of 15 microM for @entity1025 influx, with a Vmax of 0.25 nmol of @entity1025 per min per 10(8) cells. The apparent Km decreased to 3 microM, and the Vmax increased 60% after growth in a low @entity2400 concentration (10 microM). @entity515 was a simple competitive inhibitor (Ki = 30 microM) of @entity1025 influx in cells grown in high @entity1025 concentrations but blocked only a portion of the @entity1025 influx in cells grown in low @entity1025 concentrations. @entity515 influx exhibited kinetics similar to those of @entity1025 influx (Km = 30 microM; Vmax = 0.5 nmol of @entity515 per min per 10(8) cells) but was not affected by growth conditions. @entity515 influx was competitively inhibited by both @entity1025 and @entity3281 . Mutations affecting @entity1025 uptake were isolated by selection for spontaneous resistance to toxic levels of @entity515 . One class of mutants designated corA mapped at 84 min near metE with the following gene order: corA, metE, zie-3161::Tn10, pepQ. A second class designated corB mapped at 98 min near pyrB. @entity1025 influx was decreased in a corA mutant strain (relative to that of the wild type) when grown in high @entity1025 concentrations but was restored when grown in low @entity1025 concentrations. @entity515 transport was completely abolished by the corA mutation under all growth conditions. Recombinant plasmids carrying the corA region from either @entity2624 or @entity2491 complemented the corA mutation in @entity2491 , restoring uptake of both @entity515 and @entity1025 and conferring sensitivity to @entity515 . The @entity2491 corA gene was localized to a restriction fragment of approximately 1.5 kilobases.
