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My name is Barbara
Funnell and I am from
the Department of
Molecular Genetics
at the University of Toronto.
My research interests are
chromosome dynamics in bacteria
and specifically
the mechanisms of
segregation of
bacterial plasmids.
In this talk, I will
discuss plasmid segregation
or as it is more
commonly called in
bacteria partition
or partitioning.
First, I will
introduce and review
general characteristics of
plasmid partition systems and
then I will discuss,
in more detail
the mechanisms of these
events in bacteria.
My research concerns the
partition of a plasmid called
P1 in the bacteria
Escherichia coli.
I will use examples from work on
several different plasmids
including P1 during this talk.
This talk is an update from
a previous version
published in 2008
and there have been
significant developments
in the partition
field since then.
Particularly, in the structural
biology, biochemistry,
and mechanistic models,
and in the variety of
partition systems that have been
identified in
bacterial plasmids.
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Plasmids as autonomous
extrachromosomal elements must
ensure their own replication and
stable maintenance in
bacterial populations,
and they use several
different types of processes.
Without them, plasmids
are lost from
the population of bacterial
cells and are thus unstable.
First, plasmid
replication systems
control copy number
to make sure that
every cell has enough
plasmid copies to
segregate to daughter cells
at the next cell division.
Second, plasmids occasionally
recombine with each
other via homologous
recombination
to produce higher multimers,
that is dimers or higher,
which reduces the number
of partitionable units.
So, plasmids often contain
specific recombination systems
to resolve these
back into monomers.
Perhaps the most
famous of these is
the lox-cre recombinase
pair from the P1 plasmid,
which has been exploited very
successfully for
genetic engineering.
Third, plasmids in code,
what are often called
addiction systems,
these consist of
a bacterial toxin
and antitoxin which kill
cells that lose the
plasmid because
the antitoxin is less
stable than the toxin.
Fourth, and the subject of
this talk, the partition
systems which make sure that
enough plasmids are
in the right place in
the cell so that
every daughter cell
receives at least one copy.
That is, the partition is
a transport and
positioning process
where the cargo is plasmid DNA.
