plasmid ori's

Julian Parkhill J.Parkhill at
Wed Sep 4 12:00:23 EST 1996

In article <50k7gh$eb1 at>, DENTON at (Rex
Denton) wrote:

> In <322DA45A.397E at> David writes:
> > Hi,
> > I was wondering what would happen if you have two different but 
> > compatible ori's (eg colE1 from pBluescript and oriF) on the same 
> > plasmid. Will one be dominant over the other?, and if so does anyone 
> > know which one is dominant? Another thing is there any way to select for 
> > oriF-carrying vectors over colE1-carrying vectors with the same 
> > antibiotic resistance?
> Hi,
> Simple answer- E.Coli will only tolerate *one* origin of replication. 
> that have two will not replicate.  If the host was rec A + it might try to
> remove one or the other oris but, since most hosts used for cloning are RecA-
> (for obvious reasons) this won't happen.
> Rex

Sorry, but that is not true. I have a plasmid (pPOD6, used for generating
hybrids between homologous genes) that has two functional origins of
replication (ColE1 and p15). I don't know what exactly happens (in terms
of which is dominant) when they are both on the same plasmid, but when
that plasmid is allowed to recombine it produces two plasmids, each
replicating from a different ori.
In addition, I have often cloned the backbone from one plasmid into
another, resulting in a stable plasmid with two ori's.


          Julian Parkhill   -   J.Parkhill at
   CRC Laboratories, Inst. of Cancer Studies, Medical School,
 University of Birmingham, Edgbaston, Birmingham, B15 2TJ, U.K.
Disclaimer: If I thought anybody gave a damn about my opinions....

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