HELP! selective scission - thrombin digestion (Nov/16/2005 )

I have cloned my gene of interest into pGEX-4T-1, and the induciton of GST fusion protein works fine. Today I am so surprised that thrombin acturally recognizes lots of peptide sequences. One of them, which is Arg-Gly, is present in the N-terminus of my protein!!!!

Does anyone of you know condition that allows thrombin selective digestion?
By the way, the designed cutting sequence between GST and my protein is Lue-Val-Pro-Arg-Gly-Ser.

thanks

well, i think it's better to change vector...