CpG islands are stretches of DNA sequence that are enriched in the (CpG)n repeat 
and are present in close association with all housekeeping genes as well as some 
tissue-specific genes in the mammalian genome. Methylation of CpG islands 
strongly influences both structural organization and function of chromatin. The 
presence of a CpG island in a given chromosomal domain can, by itself, give rise 
to relatively open and active chromatin. Recently, several histone 
acetyltransferases, histone deacetylases, and chromatin remodeling factors have 
been found to be part of the transcription machinery. It is becoming 
increasingly clear that CpG islands and their methylation status may influence 
the function or recruitment of these newly discovered chromatin remodeling 
factors, especially the histone deacetylases. In addition, CpG islands may also 
play a significant role in the reorganization of chromatin during mammalian 
spermiogenesis.