Previous attempts to demonstrate repression in the system synthesizing threonine from homoserine by the addition of excess end-product gave negative results. By utilizing a mutant of Escherichia coli unable to synthesize homoserine from aspartic semialdehyde, we have shown that the threonine synthetase system is repressed when threonine is supplied at a rate that yields for the mutant organism a growth rate comparable to that of the wild-type organism in a similar medium. However, when threonine is in limited supply, this system is derepressed. That this system is normally repressed explains why earlier attempts to show repression by the addition of excess threonine were unsuccessful.
ASJC Scopus subject areas
- Molecular Biology