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P33 vs S35 for PCR sequencing

Wed Jul 13 15:05:31 EST 1994

ljohnson at udcemail.udc.upenn.edu (Lois C. Johnson) writes in article
 8 Jul 1994 <2vjpg2$h9p at netnews.upenn.edu>:

:	Does anyone have any experience using P33 for sequencing versus
:S35?  What are the radioactive hazards, i.e. exposure; Is it as a bother a
: P32 or is it treated like S35?  Is it worth the extra? cost.  I have
:heard it is more expensive thatn S35??  Has anyone out there used it for
:cycle sequencing?  All help would be appreciated.

P33 gives a signal that is > S35 but < P32.  Its energy is low enough
that there's not the shielding concern that you have for P32.  You 
should be aware that S35 comes with a major component of volatile radioactive
contaminants such that you should handle it in a chemical hood (at least
when opening the storage vial and during any heating steps).  
No kidding; I was skeptical until I put an open vial with a strong base in 
the same chamber with an open vial of S35 dATP and recovered 10^6 cpm
straight out of the atmosphere even at room temperature.  I don't 
believe that P33 or P32 have this problem.  We have used it for cycle
sequencing, but if you're using cycle sequencing to cover a sensitivity
problem, the lower signal strength of P33 tends to kill you (assuming
that you're end labelling; there are some protocols to use internal 
labelling with P33 or S35 during cycle sequencing, but we haven't tried
them).  We decided not to use P33 much because of the expense; but then
again, we have the facilities to handle the other two isotopes.  If you're
in a cramped space where effective shielding is hard and you don't have
a fume hood, then P33 might be a good safety option.

: )  Steve Hardies    Hardies at thorin.uthscsa.edu

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