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Microbiol. Mol. Biol. Rev., 12 1997, 442-455, Vol 61, No. 4
SA Khan
Many bacterial plasmids replicate by a rolling-circle (RC) mechanism. Their
replication properties have many similarities to as well as significant
differences from those of single-stranded DNA (ssDNA) coliphages, which
also replicate by an RC mechanism. Studies on a large number of RC plasmids
have revealed that they fall into several families based on homology in
their initiator proteins and leading- strand origins. The leading-strand
origins contain distinct sequences that are required for binding and
nicking by the Rep proteins. Leading- strand origins also contain domains
that are required for the initiation and termination of replication. RC
plasmids generate ssDNA intermediates during replication, since their
lagging-strand synthesis does not usually initiate until the leading strand
has been almost fully synthesized. The leading- and lagging-strand origins
are distinct, and the displaced leading-strand DNA is converted to the
double-stranded form by using solely the host proteins. The Rep proteins
encoded by RC plasmids contain specific domains that are involved in their
origin binding and nicking activities. The replication and copy number of
RC plasmids, in general, are regulated at the level of synthesis of their
Rep proteins, which are usually rate limiting for replication. Some RC Rep
proteins are known to be inactivated after supporting one round of
replication. A number of in vitro replication systems have been developed
for RC plasmids and have provided insight into the mechanism of plasmid RC
replication.
Copyright © 1997, American Society for Microbiology
Rolling-circle replication of bacterial plasmids [In Process Citation]
Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pennsylvania 15261, USA. Khan@med.pitt.edu
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