Table 2. Fidelity of Tne DNA polymerases.

Enzyme substitutions	5′→3′ exo	3′→5′ exo	Error rate (10–6)	Relative fidelity
Tne D137A/D323A	–	–	33.7	1.0
Tne D137A/D323A R722K	–	–	3.5	9.5
Tne D137A/D323A R722Y	–	–	1.9	17.7
Tne D137A	–	+	9.1	3.7
Tne D137A R722K	–	+	1.1	30.6
Tne D137A R722H	–	+	1.1	30.6
Tne D137A R722Y	–	+	1.4	24.0
Taq (WT)	+	–	7.3	4.6

Fidelity was determined by the lacZα forward assay as described in Materials and Methods. 5′→3′ exo indicates whether the exonuclease has been rendered deficient by the mutation D137A. 3′→5′ exo indicates whether the exonuclease has been rendered deficient by the mutation D323A. Wild-type Taq DNA polymerase contains only 5′→3′ exonuclease activity.