SUMMARYTransport of glutamine by the high-affinity transport system is regulated by the nitrogen status of the medium. With high concentrations of ammonia, transport is repressed; whereas with Casamino acids, transport is elevated, showing behaviour similar to glutamine synthetase . A glutamine auxotroph, lacking glutamine synthetase activity, had elevated transport activity even in the presence of high concentrations of ammonia (and glutamine). This suggests that glutamine synthetase is involved in the regulation of the transport system. A mutant with low glutamate synthase activity had low glutamine transport and glutamine synthetase activities, which could not be derepressed. A mutant in the highaffinity glutamine transport system showed normal regulation of glutamate synthase and glutamine synthetase. Possible mechanisms for this regulation are discussed.
Two classes of Salmonella typhimurium mutants resistant to inhibitory methionine analogues and defective in methionine transport have been examined. A mutant of the first class, resistant to alpha-methylmethionine, was shown by conjugation analysis to possess a single mutation in the metP gene which specifies a methionine transport system. Mutants of the second class, resistant to alpha-methylmethionine and methionine sulphoximine, possess two mutations. One is in the metP gene, which accounts for resistance to alpha-methylmethionine, and the other is in a gene designated glnP which results in reduced L-glutamine transport. Both of these mutations are required for resistance to methionine sulphoximine. A transduction analysis of three metP mutations was performed, based on the fact that they prevent growth of methionine-requiring strains on D-methionine. Two of the mutants are closely linked and therefore probably in the same gene, whereas the third mutant might be in a different gene.
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