I overexpressed a tobacco protein in E. coli using pET28. The
expression level was great for one derivative but less abundant
for a second smaller segment of the same protein. Purification
on the nickel column worked well. The protein that was produced
was virtually completely insoluble, so the the purification was
done with 6M urea. I produced enough protein for preparing
antibodies from 200 ml cells.
hope this helps-