Table 2.

ERK1s protein sequences evolve faster than ERK2s’, not their nucleotide sequences

	Vertebrate ERKs		Mammalian ERKs
	ERK1	ERK2	ERK1	ERK2
Number of codons analysed	298	298	324	322
Nucleotide substitution rate	0,221	0,210	0,091	0,080
Amino acid substitution rate	0,077	0,031	0,020	0,004
Nonsynonymous substitution rate	0,052	0,025	0,010	0,003
Synonymous substitution rate	0,640	0,717	0,321	0,322
Nonsynonymous/synonymous substitution rate	0,083	0,033	0,029	0,007
(Ka/Ks Ratio of ERK1) / (Ka/Ks Ratio of ERK2)	2,54		4,45

The synonymous substitution rates (Ks) and the non-synonymous substitution rates (Ka) of vertebrate ERKs and mammalian ERKs were calculated in MEGA6 as described in Methods