No abstract

A novel gene of Escherichia coli, rhtB, has been characterized. Amplification of this gene provides resistance to homoserine and homoserine lactone. Another E. coli gene, rhtC, provides resistance to threonine. The homologues of RhtB are widely distributed among various eubacteria and archaea, from one to 12 copies of family members that differ in their primary structure were found in the genomes. Most of them are genes that encode hypothetical transmembrane proteins. Experimental data that indicate participation of the rhtB product in the excretion of homoserine have been obtained.z 1999 Federation of European Biochemical Societies.

Overexpression of the yeaS gene encoding a protein belonging to the RhtB transporter family conferred upon cells resistance to glycyl-L L-leucine, leucine analogues, several amino acids and their analogues. yeaS overexpression promoted leucine and, to a lesser extent, methionine and histidine accumulation by the respective producing strains. Our results indicate that yeaS encodes an exporter of leucine and some other structurally unrelated amino acids. The expression of yeaS (renamed leuE for ''leucine export'') was induced by leucine, L L-a-amino-n-butyric acid and, to a lesser extent, by several other amino acids. The global regulator Lrp mediated this induction.