I am trying to express a small protein, i.e, 12 kDa with an N-terminal GST tag. I have tried various post induction time durations as well as incubation temperatures. Though I see the expression but a huge amount of only GST protein is also observed. Any clue about why the GST tag is getting cleaved? Because I don't see much of a difference in cleavage due to difference in the duration of incubation and there's no common cleavage site in the linker region.