TABLE 2.

Primers used in this study

Primer	Sequence (5′–3′)a	Description or mutations	Direction
Tg-cysF	ATCTGTTCTACTCCGGTGTGCG	5′ external primer upstream from an AflII restriction site	Forward
Tg-cysR	AGGAAACGCTGGATTTTGCGGG	3′ external primer downstream from an AfeI restriction site	Reverse
Tg-cysMutF	GAGGAGCGttgTCAGTCCAAAGAC	γH107C	Forward
Tg-cysMutR	TGGACTGAcaaCGCTCCTCGATC	γH107C	Reverse
Tg-cysMutF2	CGAACCGGACtGTGAATCGGTC	γS210C	Forward
Tg-cysMutR2	GACCGATTCACaGTCCGGTTCG	γS210C	Reverse

^a Lowercase letters indicate specific changes in the primer for site-directed mutagenesis.