Specific points on p53 exonuclease function

Thu Nov 14 08:06:10 EST 1996

Earlier this month I posted a request for information regarding the
possibility of p53 being an exonuclease for a critical review of
Mummenbrauer at al., p53 exhibits 3'-5' exonucleases activity, Cell 85. I
realise that I shouldn't have made such a general request and now have
some specific questions regarding the paper. 

1. Mummenbrauer et al use a 30-mer oligonucleotide for their gel assays of
   exonuclease activty. This sequence was found to be bound by p53 by 
   Foord et al.(1993) when part of a ds DNA fragment. Why therefore did
   Mummenbrauer use the sequence as a ssDNA oligo and not dsDNA?

2. Why did the researchers use ssDNA oligo for the gell assays and ds poly
   dA.dT for the filter binding assays?

3. If the exonuclease activity is seen with the ss 30-mer oligo then why
   doesn't ss poly dA DNA compete with the ds poy dA.dT in their assay?

4. It is stated in table 2 of the paper that p53 is acting as tetramer 
   when behaving as an exonuclease (though no evidence is put forward) but
   later on it is shown that the core domain on its own posseses 
   exonuclease activity. This contrasts with the fact that core domain was
   shown by Pavelitch et al.(1993) to be a monomer in solution. 

Thanks for your help,


Richard Jenner
King's College, Cambridge, UK.

PS Any information I recieve from this newsgroup that I use in my review
will of course be referenced to whoever posted it.

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