Taq polymerase - what exonuclease activities?

jnewton at molbiol.ox.ac.uk jnewton at molbiol.ox.ac.uk
Sun Feb 20 08:23:07 EST 1994

In article <2k57gr$t2a at charm.magnus.acs.ohio-state.edu>, wbecktel at magnus.acs.ohio-state.edu (Wayne J Becktel) writes:
> In article <1994Feb18.172239.21177 at alw.nih.gov>,
> Jim Owens  <jow at helix.nih.gov> wrote:
>>In article <CLAF5n.Is6 at massey.ac.nz> P. Hirst, PHirst at massey.ac.nz writes:
>>>I'm trying find out exactly what exonuclease activities Taq polymerase
>>>has, and which polymerase it is/ or which it's derived from.  The
>>>literature I've found so far is far from precise in its description, so
>>>any information anyone has would be greatly appreciated.
>>According to David Gelfand in Chapter 2 of PCR Technologies: Principles
>>and Applications for DNA Amplification, Henry A. Erlich (ed), Stockton
>>Press, 1989:
>>"Purified 94 kDa Taq DNA polymerase does not contain an inherent 3'-5'
>>exonuclease activity...  It is not known if T. aquaticuys contain a
>>separate 3'-5' exonuclease activity which may be associated with the
>>polymerase in vivo....  Taq DNA polymerase has a DNA synthesis-dependent,
>>strand replacement, 5'-3' exonuclease activity.  (more details omitted)"
>>Hope this helps,
>>Jim Owens
>      Taq polymerase has no exonuclease activity.  T7 DNA polymerase does in the
> native form but not in the commercial form (Sequenase).  Exo- mutants have also 
> been engineered by Patel and Johnson.  Vent polymerase has both polymerase and 
> exonuclease activity, and is thermally stable. The advantages of Vent include 
> the thermal stability and processivity.
My understanding was that Exo(-) mutants were used because the exonuclease 
activity tends to chew back di-deoxy chain terminators, which rather ruins the 
sequencing reaction. Anybody know if this is correct, or have I been labouring 
under a miss-apprehension?


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