Check for insolubility - this is important because T7 expression often leads to very high production of protein that can result in the target protein becoming insoluble. Solutions around this are:

• Induce at a lower temperature (as low as 15°C overnight)
• Reduce IPTG concentration to 40 µM
• Induce earlier in growth phase (OD₆₀₀ = 0.3 or 0.4)
• Test expression in Lemo21(DE3)