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 4 fold 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. It is proposed 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.