Purification of all proteins in an experssion library

[Mr. M.J. Lush]

	We are looking for proteins that stimulate a T-cell line.  
To do this we plan to generate a cDNA expression library and test 
the T-cells with pools of expressed proteins.

	Unfortunately bacterial proteins will also stimulate the 
T-cells, therefore we want to separate the expressed proteins from 
the bacterial ones.   What we are looking for is a tagging system
that uses a single set of conditions to purify all proteins (if it
failed to purify certain proteins they would be lost from the library)
Can anyone suggest suitable systems for this (cost is a consideration 
because we'll have to purify at least 20 pools per round of cloning).

One possibility we are considering is making a phage display library 
and purifying the M13 phage by PEG precipitation,  how good is this 
at removing bacterial contamination and are there better ways of 
purifying M13 to 'homogeneity'?

TIA^6

-- 

Michael
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NPC rights activist           |      Nameless Abominations are people too.