Biology Reference
In-Depth Information
During meiotic and mitotic DSB repair, RAD51 recruitment is dependent on
RAD52.
64,155-157
Yeast Rad52 has been shown to stimulate Rad51-mediated
strand exchange activity by mediating Rad51 NPF formation on RPA-coated
ssDNA filaments.
144-146,158
This mediator activity is critical to overcome the
inhibitory action of RPA, when RPA is added prior to Rad51. Several methods
including yeast two-hybrids, co-immunoprecipitation of whole cell extracts, and
direct protein-protein affinity pull-down techniques have shown a direct interac-
tion between Rad52 and Rad51.
91,158-160
The interaction with Rad51 is mediated
by the C-terminal 409-412 residues of Rad52.
159,161
Overexpression of Rad51
alleviates the defective RR phenotype of a
rad52
(D409-412) C-terminal deletion
mutation.
159
In vitro
and
in vivo
evidence suggests that human RAD52 interacts
with the cognate RAD51 via residues 291-330, a region that does not share
homology with yeast Rad51.
162
These results appear to imply a species-specific
interaction between RAD51 and RAD52. Rad52 has also been implicated in yeast
Rad51-independent events such as BIR and SSA.
41,86,163
Both yeast and human RAD52 have been shown to interact with
RPA.
150,164,165
Yeast two-hybrid assays indicated Rad52 interaction with all
three subunits of yeast RPA.
165
However, human RAD52 was shown to bind
directly to large (70 kD) and middle (32 kD) subunits of RPA.
164
Interestingly,
RAD52 interaction with RPA inhibits higher-order self-association of
RAD52.
164
The strand-annealing activity of both yeast and human RAD52
facilitates the second-end capture during HR repair.
166,167
Even though Rad52 plays an essential role in HR in budding yeast, in
vertebrate cells, or in cells with BRCA2 homologs, loss of
RAD52
gene leads
to few phenotypic defects in RR. RAD52 knockdown in mouse embryonic
cells and in chicken B-cell line DT40 cell lines does not cause an apparent
sensitivity to IR or DSB-causing chemical agents.
168,169
In the corn smut
Ustilago maydis
(which contains the Brh2 BRCA2 homolog), no defects in
HR were found in Rad52 mutants.
170
A recent study of human breast
cancer cell line suggests that knockdown of
RAD52
acts as a synthetically
lethal agent in the case of
BRCA2
deficiency.
171
This finding elevates RAD52
as a target for antitumorigenic therapy for breast cancer.
171,172
Amodelhas
been proposed where RAD52 functions in an alternative pathway to
BRCA2.
172
Human RAD52 does not appear to possess any RR mediator
activity
in vitro
.
85,117
However, chicken DT40 cells were nonviable and
exhibited severe HR defects in a double knockdown of
RAD52
and the
RAD51 paralog
XRCC3.
173
In addition,
U. maydis
Rad52 mutants demon-
strated an enhanced UV and IR sensitivity when their sole RAD51 paralog
rec2
was mutated.
170
Collectively, this implies that in human cells, RAD52
might function as a recombination mediator in conjunction with any one or a
combination of the RAD51 paralogs, RAD51B, RAD51C, RAD51D, XRCC2,
or XRCC3.
172
