Comparison of the proportion of genes with CpG islands in sequences upstream of the transcription start site in HKGs and non-HKGs.

*Of 2,087 genes, 2,002 UniGene clusters corresponded to upstream sequences downloaded from the UCSC site (http://hgdownload.cse.ucsc.edu/goldenPath/hg18/bigZips/).**A total of 16,850 UniGene clusters corresponded to upstream sequences downloaded from the UCSC site and the number of non-HKGs was calculated by subtracting the 2,002 HKGs from the total 16,850.CpG island criteria: length��500 bp, % GC��55, CpG o/e ratio��0.65.