Official websites use. Share sensitive information only on official, secure websites. The mechanisms of DNA transactions driven by long range protein-mediated inter and intra-chromosomal interactions are currently of considerable general interest. Here, we report that site-specific replication termination catalyzed by the dimeric Reb1 protein of Schizosaccharomyces. The interactions between two Ter sites in cis , placed in a mutually anti-parallel orientation, caused looping out of the intervening DNA in vitro and enhancement of fork arrest in vivo.
A Ter on chromosome 2 interacted pair-wise with two Ter sites located on chromosome1 by chromosome kissing. Mutational inactivation of the major interacting Ter on chromosome1 abolished or significantly reduced fork arrest at the Ter site on chromosome 2, thereby revealing a novel mechanism of control of replication termination. The process probably involves movement of chromosome segments that brings the primary binding site e.
All of the aforementioned reports were on transcriptional control. An important and interesting question that invites investigation is whether action at a distance also controls the 3 steps of DNA replication namely initiation, ongoing replication and termination.
We have previously shown that in prokaryotic plasmid systems, DNA looping controls replication initiation both positively Miron et al. The possible role of long range protein-DNA interactions in control of replication in eukaryotes previously has not been investigated. In this context, we wished to address the question as to whether two Ter sites located on 2 different chromosomes control programmed fork arrest by long range protein-DNA interactions.
The present work addresses this question. Replication termination mechanism s has been best elucidated in prokaryotes in which a replication terminator protein binds to a specific Ter sequence to impede fork movement in a polar mode. The terminator protein-Ter complexes of prokaryotes arrest replicative helicase-catalyzed DNA unwinding in one direction but allow the enzyme approaching from the opposite direction to pass through unimpeded Bastia et al. A recent review critically discusses the current status of the field including alternative models of fork arrest mechanisms Kaplan and Bastia, Physiologically programmed polar fork arrest occurs in eukaryotes in the non-transcribed spacers of rDNA from yeast to man and at certain other locations in the chromosomes, although not every replicon necessarily contains a Ter site see reviews by Kaplan and Bastia, ; Bastia and Mohanty The existing data favor a model of polar fork arrest that involves not only terminator protein-Ter interaction but also protein-protein interactions between the terminator protein and the DNA unwinding enzyme s that drive the forks Bastia et al.
