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The uptake and retention of purine bases and of uracil requires both a protonmotive force and intracellular conversion to nucleotides. Inhibition of uptake by arsenate does not imply that ATP is required for the transport process because arsenate caused a rapid fall in the level of 5-phosphoribosyl 1-pyrophosphate. A mutation defective in high-affinity adenine transport has been identified and is designated purP. This mutation has been found to lie in the neighbourhood of mtl. Competition experiments indicate that at least two other systems are used to transport guanine, xanthine and hypoxanthine.
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