QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online July 23, 2007
doi: 10.1242/10.1242/jcs.011999

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Skibbens, R. V. Articles by Eastman, L. Search for Related Content PubMed PubMed Citation Articles by Skibbens, R. V. Articles by Eastman, L. Social Bookmarking                         What's this?

Fork it over: the cohesion establishment factor Ctf7p and DNA replication

Lehigh University, Department of Biological Sciences, 111 Research Drive, Bethlehem, PA 18015, USA

View larger version (20K): [in this window] [in a new window]   Fig. 1. Cohesin structure and dynamics. Smc1p and Smc3p contain globular N- and C-termini that are aligned by the folding of a centrally positioned hinge (#). This also allows Smc1p-Smc3p binding. Mcd1p associates with SMC head domains, creating an ATP-dependent closed ring structure.

View larger version (21K): [in this window] [in a new window]   Fig. 2. Early models of sister chromatid pairing reactions. Top: `replication-coupled cohesin pairing' positions Ctf7p (red triangle) at the replication fork (DNA polymerases as hexagons) to tether together cohesin complexes as nascent sister chromatids emerge. Cohesins are depicted as rings (pre-loaded cohesin rings are shown in green; cohesin loading coincident with replication is shown in yellow) that encircle chromatin (they could also associate laterally; not shown). Several possibilities for cohesion are shown, including various cohesin ring associations or tethering by an additional factor (purple star). Bottom: `replication through a ring' allows Ctf7p-independent establishment. Here, the replication fork passes through a pre-loaded cohesin ring that entraps both sister chromatids, passively establishing cohesion.

View larger version (41K): [in this window] [in a new window]   Fig. 3. New models of cohesion establishment. Top: A replication fork moving from left to right encounters a Pds5p-decorated cohesin complex. Ctf7p is recruited to chromatin by binding either to replication fork components (RFCs, PCNA) or to Pds5p, which allows pairing reactions to occur independently of the replication fork. In single-ring models (bottom right), upon interacting with G1-loaded cohesins, Ctf7p becomes activated and either the replication fork disassembles to pass through the ring or the cohesin ring opens to allow the fork to replicate around the cohesin. Given that Ctf7p associates with chromatin at very low levels and is not restricted to the replication fork, we speculate that PCNA modification (red star) could result in both Chl1p recruitment and altered Ctf7p dynamics (e.g. release from the replication fork). In two-ring models (bottom left), Scc2p-Scc4p (not shown) deposits cohesins both during G1 phase (green ring) and S phase (yellow ring). In the simplest scenario, Ctf7p (and possibly Pds5p) coordinate cohesin-ring opening/closing reactions and deposition with replication fork progression, leading to ring-ring interactions. Ring catenation is shown for simplicity, but cohesion could involve double rings, filamentous coils or lateral cohesin association. Ctf7p-mediated pairing reactions may occur separately from the replication fork: again PCNA modifications such as SUMOylation (red star) could promote efficient cohesion establishment by recruiting Chl1p and releasing Ctf7p from the replication fork.

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

Twitter