xgpt activity

[Mats Nilsson]

Hello bionetters:

I been working with a plasmid construction including xgpt as a selectable
marker, with this we produce RNA to transfect COS cells. Now the problem is
the lack of a reliable xgpt assay.
I wonder if anyone can tell me a good and "simple" method for detection of
xgpt activity (xgpt=xanthine guanine phosphoribosyltransferase from E
Coli).
I would apreciate any references and suggestions.

Thanks a lot, 

Jorge Blackhall
Department of Medical Virology 
Uppsala University
Sweden
e-mail <proj at bio.embnet.se>