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Smallest Plasmid Origin - 393bps?

M.Alexeyev Malexeyev at biost1.thi.tmc.edu
Fri Nov 3 14:39:00 EST 1995

In article <jpcd0-0311951820000001 at>,
jpcd0 at mole.bio.cam.ac.uk (John Dixon) wrote:

> Hi all, I am after as small an origin as possible (for a plasmid rescue
> system). ColE1 seems to be 900 or so bps, we have some old vectors with
> pBR oris of 580bps, and I've just found a ref (Thomas et al Mol Gen Genet
> 1981 1-16 that talks of oriRK2 a 393bp fragment but this requires trans
> acting factors to be present in the genome of the bacteria or on another
> compatible plasmid.
> Is this the smallest ori? Can anyone point me in the right direction for
> some newer refs?

I don't know if this ori is the smallest one, but you may also consider
420 bp gamma-ori from R6K plasmid. It requires a function of the pir gene
in trans and can be propagated in both intermediate (15 per cell) and high
(appr. 225-250 per cell) depending on the allele of pir gene. This one
should be more appropriate for your purposes since RK2 (if I am not
mistaken) has copy number of 1-2 copies per cell. Also, R6K gamma-ori can
replicate fragments of DNA appr. 100 kb-long. 

Another option would be an ori from fd phage (appr 200 bp if I am not
mistaken) . This one also requires trans function. Check out Gene 130
(1993) 23-31 and references therein. I don't know the maximum size for
these vectors, though.
I hope, this will help.

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