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J. Bacteriol., 12 1996, 6888-6894, Vol 178, No. 23
D Henderson and RJ Meyer
The broad-host-range plasmid R1162 is conjugally mobilized at high
frequency by the IncP-1 plasmid R751 but is poorly mobilized by pOX38, a
derivative of the F factor. In both cases, the origin of transfer (oriT)
and the Mob proteins of R1162 are required, indicating that these plasmids
are mobilized by similar mechanisms. R1162 encodes a primase, essential for
vegetative replication of the plasmid, that is made both as a separate
protein and as the carboxy-terminal domain of MobA, one of the R1162
mobilization proteins (P. Scholz, V. Haring, B. Wittman-Liebold, K. Ashman,
M. Bagdasarian, and E. Scherzinger, Gene 75:271-288, 1989). When R751 is
the mobilizing vector, the primase is not required for mobilization of
plasmids containing cloned mob-oriT R1162 DNA. However, detectable
mobilization of such plasmids by pOX38 requires both the primase and its
cognate initiation site, oriented for synthesis of the complement to the
transferred strand. The long form of the primase is required for optimal
transfer: R1162 replicons lacking this form also are not transferred
detectably by pOX38 and are less well mobilized by R751. The distance
between oriT and the primase initiation site affects the frequency of
mobilization, and this effect is polar in the direction of transfer. Our
results indicate that the R1162 primase is active in mobilization of R1162
and suggest that the MobA-linked form is an adaptation increasing its
effectiveness during transfer.
Copyright © 1996, American Society for Microbiology
The primase of broad-host-range plasmid R1162 is active in conjugal transfer
Department of Microbiology, University of Texas at Austin, 78712, USA.
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