Open AccessIntracellular Trp repressor levels in Escherichia coli
Author(s) -
Robert P. Gunsalus,
Antonio H. Miguel,
Glen L. Gunsalus
Publication year - 1986
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.167.1.272-278.1986
Subject(s) - repressor , intracellular , biology , tryptophan , escherichia coli , extracellular , trp operon , biochemistry , microbiology and biotechnology , gene , gene expression , lac operon , amino acid
A radioimmunoassay for the Trp repressor protein of Escherichia coli was developed with antisera raised against purified Trp repressor protein. This assay was used to directly measure the intracellular Trp repressor content in several E. coli K-12 and B/r strains. Repressor levels varied from 2.5- to 3-fold in response to L-tryptophan concentration in the growth medium (15 to 44 ng of repressor per mg of protein). Neither cell growth rate nor culture age had a significant effect on repressor concentrations within the cell. Addition of L-tryptophan to the growth medium resulted in lowered intracellular levels of Trp repressor. The absolute amounts of native Trp repressor molecules per cell varied between 120 and 375 dimers in the presence and absence of L-tryptophan in the culture medium, respectively. Assuming an intracellular volume of 7.3 microliters/10(10) E. coli cells, the Trp repressor concentration varied from 270 to 850 nM in response to extracellular tryptophan levels. These findings represent the first direct measurements of Trp repressor levels in E. coli and confirm the autoregulatory nature of the trpR gene.