I recently cotransformed a plasmid that contains my gene of interest with Groel/S Chaperones in BL21 (DE3). After I got so many colonies I expressed in 1L of LB and induced using o.5mM IPTG 20 degrees overnight, but the surprise was that the protein pellet I got had orange color! I also had very little expression, so my question is why I got that color?Is it possibly a contamination? Should I use higher temperatures to coexpress with chaperones?
I wouldn't care about the color of the pellet. What important is where your protein. If the pellet is orange but you you don't have your protein in there, why bother.
I have some E. coli plates that have some orange colonies, but they only visible after I let the plates stood for over two weeks or so, because the colonies were big at that time. So you can consider contamination has happened.
My rule of thumb is always start with standard conditions: 37C, 1mM IPTG, and see how my protein is expressed. If it's expressed badly (only few), I wouldn't star playing around with IPTG concentrations or temperature.
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