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Journal of Bacteriology, May 1999, p. 2765-2772, Vol. 181, No. 9
Department of Microbiology, University of
Melbourne, Parkville, Victoria 3052, Australia
Received 29 September 1998/Accepted 16 February 1999
Replication of the IncB plasmid pMU720 requires the synthesis of
the cis-acting RepA protein and the presence of two DNA
elements, ori and CIS. CIS is the 166-bp
sequence separating the RepA coding sequence from ori. To
investigate how this organization of the pMU720 replicon contributes to
the mechanism of initiation of replication, mutations in the sequence
and/or the length of CIS were introduced into the
CIS region and their effects on the efficiency of
replication of the pMU720 replicon in vivo was determined. The
CIS region was found to be composed of two domains. The
repA-proximal domain, which showed strong transcription
termination activity, could be replaced by equivalent sequences from
I-complex and IncL/M plasmids, whose replicons are organized in the
same fashion as pMU720. Replacement by a trpA transcription
terminator afforded only partial replication activity. The
repA-distal domain was shown to be a spacer whose role was
to position sequence(s) within ori on the correct face of
the DNA helix vis-à-vis the repA-proximal portion of
CIS. A model for the loading of RepA protein onto
ori is discussed.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Role of CIS in Replication of an
IncB Plasmid
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, University of Melbourne, Royal Parade,
Parkville, Victoria 3052, Australia. Phone: 61 3 9344 5679. Fax: 61 3 9347 1540. E-mail:
aj.pittard{at}microbiology.unimelb.edu.au.
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