DNA strand asymetry in coding regions.

Brian Foley brianf at med.uvm.edu
Wed Jan 19 08:53:38 EST 1994


	Can someone point me to a recent article on strand asymetry in DNA
damage, repair, or mutations?  I'm looking at some genes which have
undergone a lot of mutations at CpG sites.  CpG becomes methylated in mammals
then the 5-methyl-C can deaminate to become a T, which is not repaired by
damage-recognition enzymes because it is not damage, it is just a mispairing.
	Anyway, if the C on one strand mutaties at the same rate as the
C on the other strand we should see an equal number of CpG -> TpG
mutations and CpG -> CpA mutations.  This is not the case.  There are
many more CpG -> TpG mutations.  
	The statistical analysis is a bear because the CpG dinucleotide does
no occur in all reading frames equally.  If CpG occurs mainly with the C of
the mRNA-like (noncoding) strand in the third position of the codons this
means that the G is in the first position of a codon and the G -> A will
result in (Val -> Leu, Ala -> Pro and so on) amino acid changes.  Thus I
need to take this into account when deciding if I am seeing strand asymetry
of repair, or just selection against amino acid changes.

 --
********************************************************************
*  Brian Foley               *     If we knew what we were doing   *
*  Molecular Genetics Dept.  *     it wouldn't be called research  *
*  University of Vermont     *                                     *
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