Membrane association of leucyl-tRNA synthetase during leucine starvation in Escherichia coli.

The influence of leucine starvation on the subcellular location of leucyl-tRNA synthetase in Escherichia coli was examined in a leucine auxotrophic strain by sucrose density sedimentation analysis. Analysis of the subcellular distribution of leucyl-tRNA synthetase activity revealed that during unrestricted growth, the leucine synthetase enzyme activity was found to be localized in the soluble protein fraction of the gradient. However, during restricted growth on low levels of leucine, leucyl-tRNA synthetase activity was localized in the cytoplasmic membrane fraction of the gradient. The transition from soluble to membrane-association of the enzyme also occurred following inhibition of protein synthesis by treatment of cells with chloramphenicol. These results collectively suggest that leucyl-tRNA synthetase may be recruited to the cytoplasmic membrane in response to shortages of leucine or perturbation of protein synthesis.