Hey there, currently I am working on threonine synthase enzyme of Leishmania. I have successfully cloned it into E.coli DH5alpha strain. I have also transformed it into E.coli BL21(DE3) strain. I tried induction at 37°C and 25°C with IPTG concentration 0.1mM, 0.5mM and 1mM respectively. At 25°C with IPTG concentration 0.1mM after purification I got very faint band of expected size ~75kDa and it was confirmed by western blot analysis too. But the problem is that yield is very low. How I can maximize the yield? How the recombinant protein expression is increased in E.coli BL21(DE3) strain? Can anyone suggest paper on this ? My protein molecular weight is ~75kDa and it is His tagged protein.