Housekeeping genes tend to show reduced upstream sequence conservation

Table 1 Sequence divergence versus tissue expression breadth

No. of tissues	N (total = 3,893)	d_SM	Kp	Ka	Ks	Ka/Ks
01-10	986	0.688	0.337	0.107	0.733	0.150
		0.735	0.328	0.084	0.673	0.119
		0.221	0.110	0.093	0.299	0.122
11-50	1,889	0.701	0.333	0.079	0.708	0.116
		0.752	0.328	0.058	0.633	0.089
		0.216	0.093	0.073	0.307	0.103
51-55	1,018	0.732	0.328	0.050	0.639	0.079
		0.791	0.323	0.031	0.572	0.054
		0.208	0.079	0.057	0.305	0.085
	p value (K-W test)	<10^-5	0.226	<10^-75	<10^-18	<10^-62

N, number of genes; d_SM, promoter divergence (see text); Kp, promoter substitution rate; Ka, non-synonymous substitution rate; Ks, synonymous substitution rate. Mean (top), median (middle), and standard deviation (bottom) are indicated for each variable. Numbers in bold indicate significant differences at p < 0.001 in each expression group with respect to the rest (two-sample Wilcoxon-Mann-Whitney test). The last row shows the p value of Kruskal-Wallis (K-W) test that evaluates differences between the three tissue expression breadth groups.

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