Homologous recombination (HR) repairs chromosome
damage and is indispensable for
tumor suppression in humans. RAD51 mediates
the DNA strand-pairing step in HR. RAD51
associated protein 1 (RAD51AP1) is a RAD51-interacting
protein whose function has remained
elusive. Knockdown of RAD51AP1 in human
cells by RNA interference engenders sensitivity
to different types of genotoxic stress, and
RAD51AP1 is epistatic to theHRprotein XRCC3.
Moreover, RAD51AP1-depleted cells are impaired
for the recombinational repair of a DNA
double-strand break and exhibit chromatid
breaks both spontaneously and upon DNAdamaging
treatment. Purified RAD51AP1 binds
both dsDNA and a D loop structure and, only
when able to interact with RAD51, greatly stimulates
the RAD51-mediated D loop reaction.
Biochemical and cytological results show that
RAD51AP1 functions at a step subsequent to
the assembly of the RAD51-ssDNA nucleoprotein
filament. Our findings provide evidence
that RAD51AP1 helps maintain genomic integrity
via RAD51 recombinase enhancement.