GST-fusions and proteolysis

[BIOTEC54]

I've been working with several GST-fusion constructs that were built using
the pGEX-2T vector. While I usually see good expression of my fusion
protein....upon purification via GSH affinity...I also seem to co-purify
material corresponding to the GST portion only. I'm wondering if the
inclusion of the thrombin cleavage site at the fusion junction is being
cleaved via a host protease? Has anyone removed the thrombin site and seen
only full-length protein?
Thanks
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