Precipitating bactriophage

[DANIEL Y KIM]

Hello:

I have been trying to construct a filamentous phage display of a protein 
fused to M13 gene III.  In my plasmid/phagemid, the gene III fusion is 
interrupted by an Amber stop codon.  I imagine there is a fair amount of 
protein being produced which is not fused to gene III and which will be 
secreted into the growth medium, instead of being incorporated into a 
phage particle.

Is there a way to precipitate the phage without the free protein?  It 
seems that PEG will precipitate both phage and free protein (60 kDa) out 
of the medium (positive Western signal in the absence of helper phage).  
If not, is there a convenient way to filter out the larger phage from the 
free protein?

Thanks

Daniel Kim
dkim at nmsu.edu