Volume 271, Number 40,
Issue of October 4, 1996
pp. 24836-24841
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.
A Shared, Non-canonical DNA Conformation Detected at DNA/Protein
Contact Sites and Bent DNA in the Absence of Supercoiling or Cognate
Protein Binding
(Received for publication, March 1, 1996, and in revised form, June 13, 1996)
Aris N.
Economides
,
Dan
Everdeen
and
Nikos
Panayotatos
From REGENERON Pharmaceuticals Inc., Tarrytown,
New York 10591-6707
A hybrid protein (H144), consisting of Lac
repressor and T7 endonuclease I, binds at the lac operator
and cleaves relaxed double-stranded DNA at distal but distinct sites.
These sites are shown here to coincide with a bacterial promoter, a
phage T7 promoter, a site for gyrase and intrinsically bent DNA. The
targets do not seem to share a particular DNA sequence, and in bent
DNA, cleavage occurs at the physical center rather than at the common
A-tracts. These results indicate that protein contact sites and
intrinsic bends assume a non-canonical conformation in the absence of
supercoiling or cognate protein binding. This feature may serve as a
recognition signal or facilitate protein binding to initiate
transcription and recombination.