SDS-PAGE is useful for monitoring tagged protein levels during expression and purification. Transformants expressing the desired tagged protein are identified by the absence of the parental GST and by the presence of a novel, larger tagged protein. Parental pGEX vectors produce a Mr 29 000 GST-tagged protein containing amino acids coded for by the pGEX multiple cloning site.
DTT should be freshly prepared and added to the sample loading buffer just before adding the sample loading buffer to the samples. β-mercaptoethanol (500 µL per 10 mL) can be used as an alternative to DTT.