Table S2.

Fidelity of the WT and 24-3 polymerases

Polymerase	Expected	Observed (%)
		A	C	G	U	Del	Ins
WT	A	91.3	1.0	1.4	0.1	6.2	0.0
	C	0.0	99.1	0.1	0.8	0.0	0.0
	G	0.1	0.7	99.0	0.2	0.0	0.0
	U	0.7	0.2	1.6	97.4	0.1	0.1
24-3	A	81.1	0.4	7.4	0.4	10.7	0.0
	C	0.2	93.3	0.2	6.0	0.3	0.0
	G	0.3	0.6	98.2	0.2	0.6	0.0
	U	0.4	0.4	1.5	96.5	1.3	0.1

Operating on the favorable template 3′-ACGCUUCGCAC-5′, the average fidelities of WT and 24-3 were 96.6% and 92.0%, respectively, calculated as the geometric mean of the fidelities for each templating base, including deletions. Excluding wobble mutations, the fidelities were 97.2% and 95.5%, respectively. Bold values indicate correct nt incorporation.