Computationally Comparative Analysis of CpG Islands in Human Bidirectional and Unidirectional Promoters

Bidirectional gene pairs have received considerable attention because this unique genomic organization is so prevalent in vertebrate genome that it covers more than 10% of the whole genes in human. To study the character of these adjacent head-to-head gene pairs and to improve the understanding of the difference between bi- and unidirectional genes, we identified all the bidirectional gene pair members based on the latest genome assembly data in 2009, analyzed their intergenetic promoter regions and evaluated the functional enrichment of bidirectional genes and function association between pair members. Our results elucidated that much more GC-content and CpG islands were observed in the promoter regions of bidirectional genes compared to those in unidirectional ones. Further, function of bidirectional genes were tend to associated in metabolism process and energy transfer and pair members were likely to share some gene ontology, which imply coordinate regulation resulting in co-expression of them. Our analyses systematically investigated the inner properties of bidirectional gene pairs as a specific architecture in human genome, allowing further verification and validation of their exact molecular mechanism.