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Journal of Bacteriology, April 2001, p. 2476-2484, Vol. 183, No. 8
Institute of Molecular and Cellular
Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo
113-0032,1 and Department of Molecular
Genetics, Institute of Molecular and Cellular Biology for
Pharmaceutical Sciences, Kyoto Pharmaceutical University,
Yamashina-ku, Kyoto 607-8412,2 Japan
Received 27 November 2000/Accepted 30 January 2001
IS1, the smallest active transposable element in
bacteria, encodes a transposase that promotes inter- and intramolecular
transposition. Host-encoded factors, e.g., histone-like proteins HU and
integration host factor (IHF), are involved in the transposition
reactions of some bacterial transposable elements. Host factors
involved in the IS1 transposition reaction, however, are
not known. We show that a plasmid with an IS1 derivative
that efficiently produces transposase did not generate miniplasmids,
the products of intramolecular transposition, in mutants deficient in a
nucleoid-associated DNA-binding protein, H-NS, but did generate them in
mutants deficient in histone-like proteins HU, IHF, Fis, and StpA. Nor
did IS1 transpose intermolecularly to the target plasmid in
the H-NS-deficient mutant. The hns mutation did not affect
transcription from the indigenous promoter of IS1 for the
expression of the transposase gene. These findings show that
transpositional recombination mediated by IS1 requires H-NS but does not require the HU, IHF, Fis, or StpA protein in vivo. Gel
retardation assays of restriction fragments of IS1-carrying plasmid DNA showed that no sites were bound preferentially by H-NS
within the IS1 sequence. The central domain of H-NS, which is involved in dimerization and/or oligomerization of the H-NS protein,
was important for the intramolecular transposition of IS1,
but the N- and C-terminal domains, which are involved in the repression
of certain genes and DNA binding, respectively, were not. The SOS
response induced by the IS1 transposase was absent in the
H-NS-deficient mutant strain but was present in the wild-type strain.
We discuss the possibility that H-NS promotes the formation of an
active IS1 DNA-transposase complex in which the
IS1 ends are cleaved to initiate transpositional
recombination through interaction with IS1 transposase.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.8.2476-2484.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Involvement of H-NS in Transpositional
Recombination Mediated by IS1
*
Corresponding author. Mailing address: Institute of
Molecular and Cellular Biosciences, The University of Tokyo, Yayoi
1-1-1, Bunkyo-ku, Tokyo 113-0032, Japan. Phone: 81-3-5841-7852. Fax: 81-3-5841-8484. E-mail: eohtsubo{at}ims.u-tokyo.ac.jp.
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