The Replication Band of Ciliated Protozoa

Abstract

Publisher Summary The replication band (RB) of ciliates is unique in cell biology. The entire complement of nuclear DNA is duplicated by a migrating, highly organized structure which can be conveniently studied using a variety of microscopy techniques. Most other eukaryotic nuclei exhibit hundreds of dispersed foci of replication which activate at different times during the S-phase. RBs initiate at species-distinctive positions within the ciliate macronucleus, signaling the beginning of the S-phase, and progress as a wave of chromatin modification and replication, which disappears at the termination of the S-phase. Throughout this entire period of migration and DNA replication, the RB maintains a remarkable ultrastructural stratification spanning the diameter of the MAC. These regular fibers disperse at the junction with the rear zone, which is the site of DNA synthesis. Condensed chromatin reappears at the distal end of the RZ. In the RB, the temporal events of DNA synthesis and chromatin assembly are displayed in a vectorial fashion. This vectorial property forms the basis for a significant scientific utility; namely, cytochemical and immunochemical mapping of chromatin replication components and events.