Table 4. Enzymatic activity of THI3 mutants.

Activity was determined in the lysates from E. coli cells transformed with plasmids containing the THI3 sequence with indicated amino acid substitutions. The expression levels of all mutants were similar to that of wild-type protein as judged from immunochemical analysis using CBD-specific antibodies (results not shown). The activities were expressed relatively to those determined in the wild-type protein samples. Values given are ranges from at least three independent experiments.

	Relative activity (%)
Mutant	TMP synthase	HMP kinase
Q98L	104–124	0–2
M134K	97–111	0–5
Q373L	96–113	64–75
S444A	0–1	80–91
T472D	101–126	46–54
Q98L/Q373L	93–105	7–13
M134K/T472D	83–97	19–32