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J. Bacteriol., Apr 1997, 2339-2347, Vol 179, No. 7
JW Wilson, EA Sia and DH Figurski
Eight coordinately regulated operons constitute the kor regulon of the IncP
alpha plasmid RK2. Three operons specify functions required for replication
initiation, conjugative transfer, and control of gene expression. The
functions of the other operons, including those of the four coregulated
operons that compose the kilA, kilC, and kilE loci, have not been
determined. Here, we present the first evidence that a kil determinant is
involved in IncP plasmid maintenance. Elevation of KorC levels specifically
to reduce the expression of the KorC-regulated kilC and kilE operons
severely affected the maintenance of both the IncP alpha plasmid RK2lac and
the IncP beta plasmid R751 in Pseudomonas aeruginosa but had little effect
on plasmid maintenance in Escherichia coli. Precise deletion of the two
kilE operons from RK2lac was achieved with the VEX mutagenesis system for
large genomes. The resulting plasmid showed significant loss of stability
in P. aeruginosa only. The defect could be complemented by reintroduction
of kilE at a different position on the plasmid. The instability of the
RK2lac delta kilE mutant did not result from a reduction in average plasmid
copy number, reduced expression of kilC, decreased conjugative transfer, or
loss of the korE regulator. We found that both the par and kilE loci are
required for full stability of RK2lac in P. aeruginosa and that the par and
kilE functions act independently. These results demonstrate a critical role
for the kilE locus in the stable inheritance of RK2 in P. aeruginosa.
Copyright © 1997, American Society for Microbiology
The kilE locus of promiscuous IncP alpha plasmid RK2 is required for stable maintenance in Pseudomonas aeruginosa
Department of Microbiology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
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