Protein purification by affinity tags

[Yu Wai Chen]

Hello,

This is a general question about making fusion protein for affinity
purification.  Several protein purification systems offer a choice of N-
or C- terminal fusion of affinity tags, such as CBD, His6 etc while
other systems have only N-terminal tags, such as GST, MBP.  It is
obvious that if the tag is at the N-terminus, one can get truncated
protein products bound onto the affinity column.  If the tag is
C-terminal, only full-length fusion protein will be retented.  With such
consideration, why would so many affinity tags be made to the
N-terminus?  It seems to me that it offers no advantage at all...

Please comment.
-- 
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Yu Wai CHEN, Ph.D. ..................  email: ywc at mrc-lmb.cam.ac.uk
 Centre for Protein Engineering,              tel: 44-(1223) 402148
 MRC Centre, Cambridge  CB2 2QH, U.K.         fax: 44-(1223) 402140
 WWW homepage: http://www.mrc-cpe.cam.ac.uk/people/wai.html