Perichromatin region: a moveable feast.

The perichromatin region is an elusive zone of the cell nucleus located at the periphery of the condensed chromatin areas. This region is visible at the electron microscope level under special staining treatments, otherwise it is merged with the border of condensed chromatin. In this 200 nm-thick area, several fundamental cell processes take place, such as replication, DNA repair and transcription. In addition, RNA processing occurs in the perichromatin region, including 5'-capping and 3'-polyadenylation as well as splicing. Recently, it has become clear that also some epigenetics modifications take place there, such as methylation of DNA and RNA on cytosine and adenosine. In summary, this thin interface between chromatin and the interchromatinic space represents the zone where the majority of the functions of DNA in interphase occur, in a place where there is no steric hindrance of condensed chromatin, the products can easily move away toward their target and the enzymes can freely dock.