Termination at sTop2

Abstract

In this issue of Molecular Cell, Fachinetti et al. provide the first comprehensive map of replication termination sites (TERs) in Saccharomyces cerevisiae (Fachinetti et al., 2010). Strikingly, the majority of TERs are occupied by topoisomerase 2, which shields these regions against genomic instability.

Figure 1

Organization of Ter sites in E. coli and eukaryotic TERs. A) The red bar marks the origin of replication, oriC. The red arrows indicate the direction of replication and black arrowheads indicate the Ter sites and their orientation. Shown in cyan is a crystal structure of the Tus protein (PDB file 2I05). B) Two replication forks converging on a TER are shown. TERs are approximately 5kb in length and are associated with Top2 (orange; PDB file 1PVG). Three classes of TERs were identified: (I) a subset with RNA polymerase II (green; PDB file 1I6H) binding sites, (II) a subset with RNA polymerase III binding sites, including long terminal repeats (LTR), transposon (TY) elements, and tRNA genes, and (III) a subset of sites that contain a centromere (CEN).