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Three mutants of Salmonella typhimurium LT2, which required either pantothenate or beta-alanine for growth, were obtained after treatment with N-methyl-N'-nitro-N-nitrosoguanidine. Their phenotype was: SM30 Pan-, SM31 Pan- Met-, SM32 Pan- Thi- (requirement for the thiazole-moiety of thiamine). Neither aspartate, dihydrouracil, nor beta-ureidopropionate replaced beta-alanine as growth factor. By conjugation it was found that the three genetic lesions (Pan-, Met-, Thi-) were located at about minute 128 of the bacterial chromosome. By transduction 63% linkage was found between the Pan and Met loci, and 84% between the Thi and Pan loci. Probably the thiazole auxotrophy was due to a lesion in the thiG locus. The new genetic locus responsible for the synthesis of beta-alanine was named panD.

Communications to the Editor 4437 in comparison with the capacity for de novo synthesis, were used in this experiment.

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