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Thermophilic Bacteria

Alastair Hamilton ah8 at stir.ac.uk
Wed Nov 4 15:28:26 EST 1998

Hi Gilbert,
'Taq' is an abreviation for Taq DNA polymerase.  It is the enzyme most 
commonly used in PCR (there are others, esp for specialist purposes).
The most important characteristic is that, originating as it does from an 
extreme thermophile, the enzyme is extremely thermostable.  Its 
temperature optimum is 72C, more importantly, it is not immediately 
denatured by the 94C (or so) denaturing steps that are inherent in PCR.
When PCR was first conceived of, an E.coli DNA polymerase was, at that 
time readily available, and was the obvious choice.  This meant that a 
fresh aliquot of enzyme had to be added after each denaturation step as 
it is completely denatured at 94C.
Moreover, it worked best at 37C - much lower than the annealing 
temperatures of most primers used in PCR (50-60C is usual).  This meant 
that the first attempts at PCR produced a lot of non-specific 
amplification due to mispriming at such low temperatures.
I think its fair to say that PCR developed in two stages - the first was 
the brilliant insight that was the original idea - but it was only when 
the second idea of using a thermostable enzyme came along that the 
technique became so ubiquitously useful.
Hope this helps

Alastair Hamilton
Institute of Aquaculture
University of Stirling
Scotland FK9 4LA

On Mon, 2 Nov 1998, Gilbert Douglas wrote:

> I have learned in my Sophomore biology class that one characteristic
> significant to Thermophilic bacteria is the presence of a "Taq" enzyme.  My
> question is, what reaction does this enzyme catalyze in these bacteria and
> why is this enzyme uniquely needed in the PCR?
> I would appreciate any help
> thanks,
> gilbert douglas

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