concerning your re-solubilized GST-fusion protein: are you aware of the fact
that you might have denatured your GST reporterprotein with your extraction
buffer. Sarkosyl is a strong detergent which may enfold the GST-protein.
To circumvent your problem try to grow up the E.coli cells at 30C which may
prevent the formation of inclusion bodies, but do induce them for longer
periodes, because metabolic activity is reduced at lower temperature. Also
helpfull may be to fuse only parts of your favorite protein to the GST
preferably those whith high antigenity and low hydrophobicity. A native GST-
protein exhibits as well an assayable activity, see pharmacia instruction.
good luck :-) wohi,mikn,stuttgart