Plasmid size limitation on E. Coli Transformation?

Steve Minchin S.D.Minchin at
Tue Aug 23 17:14:40 EST 1994

In article <33au8a$em5 at> brianc4208 at (BrianC4208) writes:
>From: brianc4208 at (BrianC4208)
>Subject: Plasmid size limitation on E. Coli Transformation?
>Date: 22 Aug 1994 15:28:10 -0400

>I've been having a problem transforming DH5Alpha cells with a ligation
>I've been trying.  I think the problem might be that the plasmid is just
>too darn big, somewhere < 15 KB.  I hope someone has heard of a limit,
>because I'm at a loss for any other explaination.
>Thanks for any help you can lend.

>Brian Cohen
>Albany Medical College
>brianc4208 at

Hi Brian,

I don't know what the size limit is for transformation, but  do know that the 
transformation efficiency will reduce as the plasmid size increases. However 
we do routinely transform E. coli with a low copy plasmid which is 17kb in 
size, using the standard CaCl protocol. This plasmid is nicknamed pB******D 
due the difficulty of transformation. So I'm afraid that if your plasmid is 
less than 15kb in size it should go in, but it may take several attempts. 

All the Best

Steve Minchin

Dr. Steve Minchin,

School of Biochemistry, The University of Birmingham,
Edgbaston, Birmingham, B15 2TT, U.K.

InterNet:       S.D.Minchin at
Janet:          S.D.Minchin at


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