Nucleic Acids Research, Vol 27, Issue 8 1882-1889, Copyright © 1999 by Oxford University Press
S Asano, A Higashitani and K Horiuchi
Rolling circle type DNA replication is initiated by introduction of a nick
in the leading strand of the origin by the initiator protein, which in most
cases binds covalently to the 5' end of the nick. In filamentous phage,
however, such a covalent complex has not been detected. Using a suitable
substrate and short reaction time, we show that filamentous phage initiator
gpII forms a covalent complex with nicked DNA, which rapidly dissociates
unless gpII is inactivated. A peptide-DNA complex was isolated from trypsin
digest of the complex by ion-exchange column chromatography and gel
filtration, and its peptide sequence was determined. The result indicated
that gpII was linked to DNA by the tyrosine residue at position 197 from
the N-terminus. The mutant protein in which this tyrosine was replaced by
phenylalanine did not show any detectable activity to complement gene II
amber mutant phage in vivo. In vitro, the mutant protein recognized the
origin and bent DNA as well as the wild-type does, but failed to introduce
a nick and to relax the superhelicity of cognate DNA.
ARTICLES
Filamentous phage replication initiator protein gpII forms a covalent complex with the 5' end of the nick it introduced
Division of Microbial Genetics, National Institute of Genetics, Mishima 411-8540, Japan.
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