Evidence for erosion of mouse CpG islands during mammalian evolution

Abstract

In housekeeping and many tissue-specific genes, the promoter is embedded in a so-called CpG island. We have compared the available human and mouse DNA sequences with respect to their CpG island properties. While mouse sequences showed a simple gradient distribution of G+C content and CpG densities, man had a distinct peak of sequences with typical CpG island characteristics. Pairwise comparison of 23 orthologous genes revealed that mouse almost always had a less pronounced CpG island than man, or none at all. In both species the requirements for a functional CpG island may be similar in that most DNA regions with a density of six or more CpG per 100 bp remain unmethylated. However, the mouse..