title: Regulation of amino acid transport in Escherichia coli by transcription termination factor rho.
abstract: Amino acid transport rates and amino acid binding proteins were examined in a strain containing the rho-120 mutation (formerly SuA), which has been shown to lower the rho-dependent, ribonucleic acid-activated adenosine triphosphatase activity to 9% of the rho activity in the isogenic wild-type strain. Tryptophan and proline transport, which occur by membrane-bound systems, were not altered. On the other hand, arginine, histidine, leucine, isoleucine, and valine transport were variably increased by a factor of 1.4 to 5.0. Kinetics of leucine transport showed that the LIV (leucine, isoleucine, and valine)-I (binding protein-associated) transport system is increased 8.5-fold, whereas the LIV-II (membrane-bound) system is increased 1.5-fold in the rho mutant under leucine-limited growth conditions. The leucine binding protein is increased fourfold under the same growth conditions. The difference in leucine transport in these strains was greatest during leucine-limited growth; growth on complex media repressed both strains to the same transport activity. We propose that rho-dependent transcriptional termination is important for leucine-specific repression of branched-chain amino acid transport, although rho-independent regulation, presumably by a corepressor-aporepressor-type mechanism, must also occur.
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism; D004926:Escherichia coli / Q000254:growth & development / Q000378:metabolism*; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D009154:Mutation; D012234:Rho Factor / Q000502:physiology*; D013997:Time Factors; D014157:Transcription Factors / Q000502:physiology*
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D002352:Carrier Proteins; D012234:Rho Factor; D014157:Transcription Factors; D007930:Leucine