The Werner and Bloom Syndrome
Proteins Help Resolve Replication Blockage by Converting (Regressed)
Holliday Junctions to Functional Replication Forks
Amrita Machwe
Rajashree Karale
Xioahua Xu
Yilun Liu
David K. Orren
10.1021/bi2001054.s006
https://acs.figshare.com/articles/journal_contribution/The_Werner_and_Bloom_Syndrome_Proteins_Help_Resolve_Replication_Blockage_by_Converting_Regressed_Holliday_Junctions_to_Functional_Replication_Forks/2623190
Cells cope with blockage of replication fork progression
in a manner that allows DNA synthesis to be completed and genomic
instability minimized. Models for resolution of blocked replication
involve fork regression to form Holliday junction structures. The
human RecQ helicases WRN and BLM (deficient in Werner and Bloom syndromes,
respectively) are critical for maintaining genomic stability and thought
to function in accurate resolution of replication blockage. Consistent
with this notion, WRN and BLM localize to sites of blocked replication
after certain DNA-damaging treatments and exhibit enhanced activity
on replication and recombination intermediates. Here we examine the
actions of WRN and BLM on a special Holliday junction substrate reflective
of a regressed replication fork. Our results demonstrate that, in
reactions requiring ATP hydrolysis, both WRN and BLM convert this
Holliday junction substrate primarily to a four-stranded replication
fork structure, suggesting they target the Holliday junction to initiate
branch migration. In agreement, the Holliday junction binding protein
RuvA inhibits the WRN- and BLM-mediated conversion reactions. Importantly,
this conversion product is suitable for replication with its leading
daughter strand readily extended by DNA polymerases. Furthermore,
binding to and conversion of this Holliday junction are optimal at
low MgCl<sub>2</sub> concentrations, suggesting that WRN and BLM preferentially
act on the square planar (open) conformation of Holliday junctions.
Our findings suggest that, subsequent to fork regression events, WRN
and/or BLM could re-establish functional replication forks to help
overcome fork blockage. Such a function is highly consistent with
phenotypes associated with WRN- and BLM-deficient cells.
2011-08-16 00:00:00
fork regression events
form Holliday junction structures
Resolve Replication Blockage
RecQ helicases WRN
Holliday junction substrate
BLM
regressed replication fork
Holliday junction
ATP
Functional Replication ForksCells
MgCl 2 concentrations
DNA
Bloom Syndrome Proteins
replication fork progression
Holliday junction binding protein RuvA