Re. : promoter for Ampicillin in plasmids

Christopher Noren noren at
Wed Mar 30 13:24:02 EST 1994

In article <2mhim5$5ir at>, "GWDGV1::KCHOWDH"
<kchowdh at> wrote:

> Hi Kaimin,
> you can delete the ssp - sac fragment from pBS without any affect on the amp.
> selection. you  can also  use other plasmids not containing the lacz region.
> In such cases, you can select for the sucessfull insertion of lacZ by X-Gal
> staining of the transformants. Cheers, Kamal.
> Kamal Chowdhury
> Max Planck Institute
> Dept. Mol. Cell Biology
> Am Fassberg
> 37077 Goettingen
> Germany
> Tel. (49) 551-201507
> Fax. (49) 551-201504

A clarification:
The amp promoter is just upstream from the SspI site in all cloning vectors
having RTEM beta-lactamase as a selectable marker. Deletion of the
SspI-SacI fragment in pBS (or any other pUC derivative) removes the amp
promoter, but the amp gene is still expressed from the lac promoter. In
other vectors without strong promoters in the same direction as amp (e.g.
pBR322), deletion of the region upstream from the SspI site would knock out
amp resistance. So beware!

Christopher Noren
New England Biolabs
noren at

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