Precipitating bactriophage

Troels Wind wind at
Thu Jun 6 03:26:25 EST 1996

One way of obtaining pure phage particles is to do a CsCl-gradient
purification. You may have to dialyse afterwards to get rid of the
salt, but IMHO its worth the effort.

Let me know if you want a protocol, I'll try to dig it up.

Troels Wind

DANIEL Y KIM (dkim at wrote:

: 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

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