J Biol Chem, Vol. 273, Issue 9, 4921-4927, February 27, 1998
The Role of Single-stranded DNA in Flp-mediated Strand
Exchange
Xu-Dong
Zhu and
Paul D.
Sadowski
From the Department of Molecular and Medical Genetics, University
of Toronto, Toronto, Ontario M5S 1A8, Canada
The Flp recognition target site contains two
inverted 13-base pair (bp) Flp binding sequences that surround an 8-bp
core region. Flp recombinase has been shown to carry out strand
ligation independently of its ability to execute strand cleavage. Using
a synthetic activated DNA substrate bearing a 3'-phosphotyrosine group,
we have developed an assay to measure strand exchange by Flp proteins.
We have shown that wild-type Flp protein was able to catalyze strand
exchange using DNA substrates containing 8-bp duplex core sequences.
Mutant Flp proteins that are defective in either DNA bending or DNA
cleavage were also impaired in their abilities to carry out strand
exchange. The inability of these mutant proteins to execute strand
exchange could be overcome by providing a DNA substrate containing a
single-stranded core sequence. This single-stranded core sequence could
be as small as 3 nucleotides. Full activity of mutant Flp proteins in strand exchange was observed when both partner DNAs contained an
8-nucleotide single-stranded core region. Using suicide substrates, we
showed that single-stranded DNA is also important for strand exchange
reactions where Flp-mediated strand cleavage is required. These results
suggest that the ability of Flp to induce DNA bending and strand
cleavage may be crucial for strand exchange. We propose that both DNA
bending and strand cleavage may be required to separate the strands of
the core region and that single-stranded DNA in the core region might
be an intermediate in Flp-mediated DNA recombination.
Copyright © 1998 by The American Society for Biochemistry and Molecular Biology, Inc.