5'->3' exonucleases

Eric C. Kofoid kofoid at bioscience.utah.edu
Thu Mar 11 14:49:05 EST 1993


In article <C3MyGt.EM7 at ccu.umanitoba.ca> Andre Hamel,
hamel at ccu.umanitoba.ca writes:
> T4 DNA polymerase in presence of all four dNTP's can be used to "chew"
> away at 3' overhangs and to fill in 5' overhangs. It has a very active
3'
> -> 5' exo activity as well as quite processive 5'->3' pol activity.
> 
> 
> In article <1993Mar8.182657.1 at msscc.med.utah.edu>
ctwittwer at msscc.med.utah.edu writes:
> >Exonuclease III from E. coli won't touch a 3' overhang.  I'd like to
use an
> >exo which won't touch a 5' overhang.  I had assumed that any of the
double-
> >strand specific 5'->3' exo's such as lambda exo and T7 gene 6 would do
the
> >trick.  I looked into it a bit, and I have the impression that both of
these
> >enzymes will in fact chew from a 5' overhang.  Is this impression
correct?
> >Is there any exo which will do what I want?  What's the deal with the
5'->3' 
> >exo activity of DNA polymerase 1?
> >
> >-Josh Cherry
> >
> 
> 

T7 DNA polymerase has a similar set of activities (and absences thereof). 
Both enzymes, acting as exonucleases, chew base-paired 3' ends much more 
slowly than they do single-stranded 3' ends. Thus, they are of limited
use 
in gap propagation or creation of nested deletions. On the other hand,
I'm 
not sure if anyone has ever tried to optimize the reactions for such 
purposes.

Cheers,

Eric
--------------------------------------- Eric Kofoid
     "When the wind blows,            | Dept. Biology, U. of Utah
          even turkeys can fly"       | SLC, UT 84112
                                      | kofoid at biology.utah.edu



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