Genomic regions and CG islands were defined based on NCBI build 36/hg18 coordinates downloaded from the UCSC website. Promoters were arbitrarily defined as transcriptional start site ± 500 bp or 2,000 bp for each Ref Seq transcript (as indicated in the text). According to the UCSC annotation many Ref Seq transcripts can be associated with a given gene, and they can have the same or alternative transcriptional start site. Gene bodies are defined as the transcribed regions, from the start to the end of transcription sites for each Ref Seq.
