Can multiple plasmids comete in transfections?

Ian A. York iayork at
Tue Mar 19 10:11:14 EST 2002

In article <c09b237b.0203152132.1230619d at>,
John Ladasky <ladasky at> wrote:
>with CFP.  In both cases, I've observed an extremely annoying pattern:
>those cells which are CFP-bright are YFP-dim, and vice versa.  This is

We see the same thing.  We believe that the problem is not so much that 
the plasmids don't get into the cell (at least, not with two plasmids; 
when we go to three or more plasmids, we think that becomes an important 
factor), but rather there's competition for protein expression.

>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

This is our feeling, too.  I've heard other people saying the same thing, 
but I don't know if it's been proven, or published.  

On the other hand, we've also tried using different promoters (CMV and 
RSV, for example) and we haven't been impressed by those results either.

So I don't have a solution, but I can sympathize.

    Ian York   (iayork at  <>
    "-but as he was a York, I am rather inclined to suppose him a
     very respectable Man." -Jane Austen, The History of England

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