Large plasmid inserts, electroporation

ladasky at ladasky at
Thu May 4 02:13:44 EST 2000

In article <3910F14D.67D24DC0 at>,
  wgallin at wrote:

> At 05:32 PM 5/3/00 +0100, yan wu wrote:
> >I am looking for plasmid or phagemid vector(s) which
> >can hold 50kb DNA insert. I
> >appreciate it very much if anybody can send me
> >information about the name of the plasmid
> >and the place I can get it. Thank you very much. My
> For that size people have typically used cosmids.  The only difference
> between cosmids and plasmids is the inclusion of the lambda cos site
> in the vector, allowing packaging into a lambda phage particle for
> easy transfection of the bacteria.  The high transformation rate is
> mainly important for making libraries.
> However, why not clone into your plasmid of choice and electroporate
> to transfect your bacteria.  It may not be the most efficient method,
> but if you are not making libraries it probably won't matter.
>     As far as I know there is nothing special about plasmids that
> prevents them from holding a big insert.  The reason people haven't
> used them for that, historically, is that the chemical transfections
> are size-limiting.  I don't think electroporation is.
> Warren Gallin

I can corroborate part of Warren's remarks.  I was going through some
old magazines recently, and came across a 1983 Scientific American
article on plasmids.  The article described several naturally-occurring
plasmids in E. coli whose sizes had been determined by restriction
mapping, and were on the order of 80 to 100 kB.

John J. Ladasky Jr., Ph.D.
Department of Structural Biology
Stanford University Medical Center
Stanford, CA 94305

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