Can multiple plasmids comete in transfections?

Pamela Norton at
Tue Mar 19 13:09:43 EST 2002

In article <c09b237b.0203152132.1230619d at>, John
Ladasky <ladasky at> wrote:

> All of my plasmids are built from Clontech's pN3 vector.  Therefore I
> have the same eukaryotic promoter in each plasmid, the ever-popular
> human cytomegalovirus immediate early promoter (pCMV-IE).  One of my
> colleagues suggests that a transcription factor which binds pCMV-IE
> may be in limited supply.  Thus, when I succeed in obtaining a high
> level of expression from one promoter, it comes at the expense of the
> other promoter.  This seems plausible to me.  Does anyone out there
> know if such a phenomenon has been reported?  I'm combing Medline, but
> as you might imagine, a keyword search with the terms "promoter",
> "competition", and "transfection" is awfully broad...

This seems plausible to me as well. I have some colleagues who have
looked in some detail at the ability of transfections to saturate with
respect to gene expression. Their results suggest that transfections
can max out at less than <1 ug DNA, although this is undoubtedly cell
type dependent. How much plasmid are you using? 

Also, you might want to look at:

Konopka et al. Rev-binding aptamer and CMV promoter act as decoys to
inhibit HIV replication. Gene 2000 Sep 19;255(2):235-44

Pam Norton

> If you can think of any other reasons why I might be seeing negative
> correlation between the expression levels of the two proteins, that
> would be useful as well.
> Thanks again!
> --
> John J. Ladasky Jr., Ph.D.
> Department of Biology
> Johns Hopkins University
> Baltimore MD 21218
> Earth

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