Table 1.

Numbers and mutational spectra of base substitutions according to genetic background

Substitution	Ancestor	mutT	mutT mutY-E	mutT mutY-L
A:T→T:A	5 (1, 4, 0)	0	0	0
A:T→C:G	8 (1, 5, 2)	412 (48, 307, 57)	233 (32, 159, 42)	292 (41, 205, 46)
A:T→G:C	6 (0, 2, 4)	0	1 (0, 1, 0)	1 (0, 1, 0)
C:G→T:A	15 (0, 13, 2)	0	2 (1, 1, 0)	2 (1, 1, 0)
C:G→G:C	2 (0, 2, 0)	0	0	0
C:G→A:T	5 (0, 3, 2)	2 (0, 2, 0)	38 (13, 18, 7)	24 (6, 15, 3)
Total	41 (2, 29, 10)	414 (48, 309, 57)	274 (46, 179, 49)	319 (48, 222, 49)

Point mutations along all branches in the phylogenetic tree for each background (i.e., branches of the same color in Fig. 1A). Numbers in parentheses show the separate counts for synonymous, nonsynonymous, and noncoding mutations, respectively.