Vl. Waters et Dg. Guiney, PROCESSES AT THE NICK REGION LINK CONJUGATION, T-DNA TRANSFER AND ROLLING CIRCLE REPLICATION, Molecular microbiology, 9(6), 1993, pp. 1123-1130
Data from prokaryotic replicative and conjugative systems, which inter
relate DNA processing events initiated by a site-specific nick, are re
viewed. While the replicative systems have been established in accorda
nce with the rolling circle replication model, the mechanism of conjug
ative replication has not been elucidated experimentally. We summarize
data involving random point mutagenesis of the RK2 transfer origin (o
riT), which yielded relaxation-deficient and transfer-deficient deriva
tives having mutations exclusively in a 10bp region defined as the nic
k region. Features of the RK2 (IncP) nick region, including the DNA se
quence, nick site position, and 5' covalent attachment of the nicking
protein, have striking parallels in other systems involving nicking an
d mobilization of single-stranded DNA from a supercoiled substrate. Th
ese other systems include T-DNA transfer occurring in Agrobacterium tu
mefaciens Ti plasmid-mediated tumorigenesis in plants, and the rolling
circle replication of plasmids of Gram-positive bacteria and of phiX1
74-like bacteriophage. The structural and functional similarities sugg
est that IncP conjugative replication, originating at the oriT, and T-
DNA transfer replication, originating at the T-DNA border, produce con
tinuous strands via a rolling circle-type replication.