Werner and Bloom syndromes are genetic
RecQ helicase disorders characterized by
genomic instability. Biochemical and genetic data indicate that an important
protein interaction of WRN and
Bloom syndrome (BLM) helicases is with the structure-specific nuclease
Flap Endonuclease 1 (FEN-1), an
enzyme that is implicated in the processing of
DNA intermediates that arise during cellular DNA replication, repair and recombination. To acquire a better understanding of the interaction of WRN and BLM with
FEN-1, we have mapped the
FEN-1 binding site on the two
RecQ helicases. Both WRN and BLM bind to the extreme C-terminal 18
amino acid tail of
FEN-1 that is adjacent to the
PCNA binding site of
FEN-1. The importance of the WRN/BLM physical interaction with the
FEN-1 C-terminal tail was confirmed by functional interaction studies with catalytically active purified recombinant
FEN-1 deletion
mutant proteins that lack either the WRN/BLM binding site or the
PCNA interaction site. The distinct binding sites of WRN and
PCNA and their combined effect on
FEN-1 nuclease activity suggest that they may coordinately act with
FEN-1. WRN was shown to facilitate
FEN-1 binding to its preferred double-flap substrate through its
protein interaction with the
FEN-1 C-terminal binding site. WRN retained its ability to physically bind and stimulate acetylated
FEN-1 cleavage activity to the same extent as unacetylated
FEN-1. These studies provide new insights to the interaction of WRN and BLM helicases with
FEN-1, and how these interactions might be regulated with the PCNA-FEN-1 interaction during DNA replication and repair.