Table 1. Effects of mutations in the pyrG initially transcribed region on regulation of pyrG′-lacZ expression.

	β-Galactosidase activity*
Strain (pyrG′-lacZ genotype)	+ Cytidine	+ Orotate	Fold regulation
QM401 (wild type)	40 ± 4	600 ± 34	15
QM416 (G + 1 to A)	<1	1.4 ± 0.6
QM404 (G + 2 to A)	5 ± 0.4	1.3 ± 0.2	0.3
QM405 (G + 3 to A)	<1	<1
QM412 (C + 4 to A)	100 ± 36	200 ± 51	2
QM413 (C + 4 to T)	14 ± 2	550 ± 92	39
QM425 (G4-insertion)	960 ± 135	1990 ± 54	2

All data, except for strain QM425, are reprinted with permission from ref. 3.

^*Expressed in Miller units; mean of six determinations.