Table 1.

Complementation of the uracil requirement of strain SØ6645(ΔpyrD) by plasmids harboring wild-type and mutant pyrD genes and specific enzyme activities in extracts

Plasmid with mutation	Growth 37°C minus uracila	Growth 25°C minus uracila	Growth plus uracila	Spec. act. (U/mg)c
pFN1 (wt)	++	++	+++	0.84
pE206A	−	++	+++	0.78
pE206K	−	(−)b	+++	0.14
pK296A	−	+	+++	0.51
pK296E	−	(−)b	+++	0.14
pK206E-E296K	−	+	+++	0.63

^a Growth was monitored after ∼48 h at 25°C and after 24 h at 37°C in the absence of induction. In the presence of uracil, the colonies had approximately the same size after the two incubation periods. All plasmids seemed to complement the growth when the cells were induced, but there was a strong growth inhibition also in the presence of uracil.

^b Denotes very tiny, shadow-like colonies.

^c The cells were grown at 25°C with induction overnight. Specific enzymatic activity in noncentrifuged extracts measured by the DCIP assay. When analyzed by electrophoresis in SDS gel, the DHODA protein bands appeared equally strong in the different extracts. The background enzyme activity in extracts of the strain transformed with the vector plasmid pUHE23-2 was zero due to the deletion of the chromosomal pyrD gene of strain SØ6645.