PROTEIN EXPRESSION TESTS

pick a colony (e.g. E. coli BL21(DE3) or similar) from a recently plated transformation into ~3 mL LB with appropriate antibiotic
incubate with shaking at 37 C overnight

inoculate 50 ml LB+antibiotic with 1 mL of overnight culture
incubate with shaking at desired temperature (typically 18 or 37 C)
when OD600 is ~0.4-0.6 (mid-log): (i) remove 1 mL of culture and spin down (about 30 sec max speed in microcentrifuge) in eppendorf tube; carefully remove ALL supernatant (remove last bit with pipette) and freeze this pellet as your “pre-induction” sample (ii) add desired amount of IPTG (typically 0.1 - 1 mM)
At desired timepoints (e.g. 4 hours, overnight, etc), determine OD600 value and then prepare a “post-induction” pellet as above, using a 1 mL at OD600 = 0.5 equivalent. For example, if the OD is 1.0, you would spin down 0.5 mL instead of 1 mL

run SDS-PAGE gel of pre-induction vs post-induction samples. Hopefully this will show you a big band of expressed protein only in the post-induction sample. If so, you can go on to evaluate solubility.