CpG islands are short, dispersed regions of unmethylated DNA with a high 
frequency of CpG dinucleotides relative to the bulk genome. We have analyzed 375 
genes and 58 pseudogenes from the human entries in the EMBL Database for the 
presence of CpG islands. All 240 islands identified are associated with genes, 
and almost all cover at least a part of one exon; i.e., they are useful 
landmarks in the genome for identifying genes. More than half of the genes 
analyzed were associated with islands. All housekeeping and widely expressed 
genes have a CpG island covering the transcription start, whereas 40% of the 
genes with a tissue-specific or limited expression are associated with islands. 
In this latter group of genes, the position of the islands was not biased toward 
the 5' end of the transcription unit.