Single-strand break repair (SSBR) and base excision
repair (BER) of modified bases and abasic sites
share several players. Among them is XRCC1, an
essential scaffold protein with no enzymatic
activity, required for the coordination of both
pathways. XRCC1 is recruited to SSBR by PARP-1,
responsible for the initial recognition of the break.
The recruitment of XRCC1 to BER is still poorly
understood. Here we show by using both local and
global induction of oxidative DNA base damage that
XRCC1 participation in BER complexes can be distinguished
from that in SSBR by several criteria. We
show first that XRCC1 recruitment to BER is independent
of PARP. Second, unlike SSBR complexes
that are assembled within minutes after global
damage induction, XRCC1 is detected later in BER
patches, with kinetics consistent with the repair of
oxidized bases. Third, while XRCC1-containing foci
associated with SSBR are formed both in eu- and
heterochromatin domains, BER complexes are
assembled in patches that are essentially excluded
from heterochromatin and where the oxidized bases
are detected
