25kDa-band in pET-System-Expression

PL p at cam.ac.uk
Thu Jul 30 10:39:15 EST 1998

>In article <6ppkqs$mce$1 at gwsun.medinf.mu-luebeck.de>, "Lars Komorowski"
<larskomo at physik.mu-luebeck.de> wrote:
> I have two questions:
> 1. If the protein band is not the desired protein what can it be ?

In the pET expression system, IPTG dependent accumulation of Beta
lactamase is usually observed along with the target protein. It normally
appears as a band of +/- 31 Kda.
This induction is observed because of the inefficiency in the T7
transcription terminator: (You must have noticed that pET plasmids have
the B-lactamase gene in the same orientation as the target gene.)

The reason why the band disappears in the cytosolic fraction is because
the enzyme is secreted into the media.!!!

I hope this helps ( ,but I strongly believe this is what you are talking about.)

Good luck!


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