chemistry of Qiaex beads & DNA interaction??

[Shane Albright]

In article <5OCT199410152624 at watson.bms.com>, patel_p at watson.bms.com
(PRAMATHESH PATEL) wrote:

> Hi:
>     Does anybody know the basis of plasmid DNA interaction with the Qiaex
> beads.  If it is ionic, how come proteins or chromosomal DNA does not bind
> to the beads.  Also, I believe the washing step is just EtOH and then elute
> it with plain TE.
> 

Pramathesh,

As far as I know, the Qiaex beads are just high tech versions of powered
glass.  The protocol for their use is based on the Vogelstein & Gillespie
method; i.e., DNA binds to glass in the presence of chaotropic salts like
NaI or NaCl04, and elutes into low-salt buffers like TE.  The EtOH wash is
just to remove salts without eluting the DNA.  GeneClean is based on the
same principle.  Notice that chromosomal DNA will bind.  Proteins,
however, will not.  (Why exactly, I'm not sure. Anyone else out there
know?)

This resin is different from the one used in the plasmid purification
columns, which is an anion-exchange resin (DEAE on a silca-gel backbone). 
Therefore, lysates are loaded in low salt, washed in medium, and DNA
eluted in high salt.

Hope this answers your question.

Shane Albright