SUMMARY: A genetic locus, , located between and the operon in , and similar genes, and , near the locus of , were found to be involved in the transport of aromatic amino acids. Genetic lesions at these loci cause a variable diminution in uptake and accumulation of aromatic amino acids, alanine and glycine compared with the wild type. The F' episome carries the locus. Curing an strain of the F' episome which covers a chromosomal deletion from through the operon and regions, results in a 60 to 80 % decrease in tryptophan uptake. The introduction of F' into a operon-deleted of low transport ability restores transport ability, suggesting that in this organism may be homologous with in In , tryptophan accumulation is normally increased by prior growth in L-tryptophan, while in it is repressed. In both genera, the gene appears to have no effect on the tryptophan transport capabilities in response to changes in the concentration of L-tryptophan in the medium. Tryptophan transport in the F' hybrid was subject to repression, while in the strain which carries F' covering the equivalent chromosomal deletion, an increase in tryptophan accumulation was shown after growth in L-tryptophan-supplemented medium.


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