Hi Mo, Gene synthesis is definitely something you should try if you can afford it. However, I would suggest also trying to change expression plasmid and in particular induction system and promoter system. For toxic proteins we had some success using the pBAD (invitrogen) expression system using arabinose induction and the arabinose operon promoter different from the classical T7 promoter. It is tightly regulated and has a very fast kinetic of induction. It is worth trying even combined with gene synthesis. I also remember that some kinases are efficiently expressed in Ecoli in presence of another expression plasmid encoding two " chaperones ", the trigger factor and GroES/EL. This is worth trying too.
Hope this helps, cheers. Pascal Egea, PhD University of California San Francisco Department of Biochemistry and Biophysics Stroud Lab
