E. coli protein expression artifacts

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Iost
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E. coli protein expression artifacts

Hi,

I am having a little problem with recombinant protein expression in E. coli: I am using pet15b and Bl21Gold, SoluBL21 and Origami cells. The plasmid is OK (sequenced) and the coding sequence has been optimized for E. coli. I even can detect a nice band on the SDS PAGE of the soluble fraction of the E. coli cells. However, this band apperars to be a protein more than 2 times the size of what I expect. I tried different denaturing conditions and reducing agents. Befor I continue to purify and sequence the protein (it runs in a region where the gel is a little crowded, so a simple "blot it and sequence it" wont work, also there no antibodies availible for this protein), I wonder if the band I see may be an artifact. I once came across a list of E. coli proteins that are more or less frequently misidentified as recombinant target proteins, but I lost the bookmark to that page. Does any one know where to find such a list, or did have a similar problem?

Thanks you very much!

Iost