| Abstract: | A spontaneous thiosine-resistant mutant of Escherichia coli was shown to have the following characteristics: lowered initial rate of lysine uptake and lowered plateau level of accumulation of exogenous lysine by both the lysine-specific and the general basic amino acid transport systems; altered repressibility of these two lysine transport systems; a derepressed level of lysine decarboxylase; normal growth rate; parental levels of lysyl-transfer ribonucleic acid synthetase and the inducible and constitutive arginine and ornithine decarboxylases. Both the mutant (lysP) and its parent (lysP+) feed a lysine auxotroph when they are plated in proximity on solid medium. However, the feeding response was observable after 1 day less of incubation when the mutant was the feeding strain. Despite the derepressed level of lysine decarboxylase in exponential cultures of the mutant extracts of these cultures had no detectable cadaverine pool. Conjugation experiments established the following gene order: gyrA (formerly nalA) lysP metG his. All thiosine-resistant recombinants assayed showed reduced lysine transport. In many of these recombinants the derepression of lysine decarboxylase was not expressed. |
