Biology Reference
In-Depth Information
downregulated in either of the deletion strains, andMMS-dependent transcrip-
tional induction of checkpoint, repair, and INO80 subunit genes was largely
unaffected in the mutant strains.
101
Outside the scope of this review, INO80 has been shown to bind to origins of
replication and be important for the recovery of stalled replication forks.
102-104
It has also been implicated in regulation of telomeres
105
and in NER of some
loci following UV exposure.
106
The first connection between INO80 and DNA repair was made when an
ino80
strain was found to be sensitive to a number of DNA-damaging agents.
Sensitivity was greatest to HU and MMS but also occurred following treatment
with UV and IR.
94
Deletion of the nonessential subunits
arp5
or
arp8
resulted
in sensitivity to MMS and HU, and hypomorphic
arp4
alleles displayed sensi-
tivity to MMS.
97,101,107,108
Given the lack of transcriptional misregulation
of repair and checkpoint genes in INO80 complex mutants, this prompted
investigation of whether INO80 has a direct role in DNA repair.
D. The Role of INO80 in DSBR
1. R
ECRUITMENT TO
DSB
S
As for RSC, a direct role of INO80 in DSBR was indicated by its recruit-
ment to DSBs. Using the HO system to generate a persistent DSB, accumu-
lation of INO80 at a break was monitored over time by ChIP. Some recruitment
of the Ino80 catalytic subunits Arp5 and Arp8 could be detected 30 min after
break induction, but enrichment continued to increase at least up to
4h.
101,108,109
In addition, Rvb1, present in both INO80 and SWR1 complexes,
was enriched adjacent to the break 45 min after break induction and Arp4,
present in both INO80 and NuA4 complexes, was enriched at the break after
2h.
108
Further analysis of the recruitment of INO80 revealed spreading of the
complex over a region of approximately 10 kb on either side of the break after
4 h, but was greatest in the immediate vicinity of the break.
107,109
Accumula-
tion of INO80 was also detected after 2 h at an HO-induced DSB elsewhere
in the genome, although the profile of enrichment differed from that found at
the
MAT
locus in that it was relatively uniform across the 5 kb adjacent to
the break.
107
2. F
ACTORS
A
FFECTING
INO80 R
ECRUITMENT
Unlike
rsc
mutants, phosphorylation of H2A S129 appears to be broadly
unaffected in
ino80
complex mutants. At 2 h following HO break formation,
when INO80 is significantly enriched near the break, H2A phosphorylation was
similar to WT levels as measured by ChIP in
ino80
,
arp5
,
arp8
, and
nhp10
deletion strains, and levels detected in Western blots after a 2-h treatment with
MMS were unaffected in
ino80
,
arp8
, and
nhp10
strains.
101,107,109,110
However,
