TABLE 2.

Mutant TyrR proteins leading to high expression of the Φ(tpl′-′lac) gene in E. coli grown in basal medium^a

tyrR allele present on pACYC177b	Sp. act. of β-galactosidase (Miller units)	Mutation(s) (putative amino acid replacement[s])
None	27.4
tyrR+	100
tyrR2c	389	GTC for V-67→GCC for A (V67A), GTT for V-499→ATT for I (V499I)
tyrR3	393	GTC for V-67→GCC for A (V67A)
tyrR4	231	GAT for D-97→GGT for G (D97G), ATT for I-402→GTT for V (I402V)
tyrR5d	863	GTC for V-67→GCC for A (V67A), TAT for Y-72→TGT for C (Y72C), GAA for E-201→GGA for G (E201G)
tyrR6	850	GTC for V-67→GCC for A (V67A), TAT for Y-72→TGT for C (Y72C), GAA for E-201→GGA for G (E201G)

^aBasal medium consists of 0.5% peptone, 0.5% meat extract, 0.5% yeast extract, and 0.2% KH₂PO₄. 

^bFour tyrR alleles (tyrR5 and tyrR6 were identical) were obtained through two different cycles of error-prone PCR. The randomly mutagenized tyrR gene was expressed under the control of its wild-type promoter on the pACYC-derived plasmid (pTK774 [see text]). 

^c25 PCR cycles. 

^d30 PCR cycles.