How to duplicate a DNA package

摘要

In a typical human cell, about two metres of DNA is wrapped around proteins to form nucleosomes, the basic units of chromatin. When this DNA is duplicated, the nucleosomes that lie ahead of the replication machinery are displaced, or disassembled into their component histone proteins. And after the machinery has passed by, the nucleosomes are reassembled on the two resulting 'daughter' strands, which requires the addition of new histones.To make things more complicated, one of the two DNA strands can be replicated only in short pieces - called Okazaki fragments - that are joined together afterwards, and so its replication lags behind that of the other strand (Fig. 1).