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DNA methylation sites

Brian H. Taylor BRIAN at BIO.TAMU.EDU
Mon May 10 20:54:06 EST 1993

    I'm wondering if anyone has ever ruled out cytosine methylation at
GC dinucleotides (as opposed to CG and CXG) or, for that matter,
CXXG. I'm familiar with the Gruenbaum et al. Nature paper from 1981
(Vol. 292, 860-862), where nearest neighbor analysis was used to show
a high level of methylation at CG and CXG.  One nonsymmetrical
arrangement, CAT, was tested and was found to be <4% methylated, but
I don't know if that means it was below their limits of detection or
they could see almost 4% methylation at those sites.  I don't think
their approach would have tested for GC symmetry.  The reason I am
asking is that I occasionally encounter cases of possible incomplete
digestion of restriction sites in genomic plant DNA with enzymes
like HindIII (recognition sequence AAGCTT).  This should not be
methylated by the usual rules, but if either GC or CXXG methylation
occurs it would block digestion.  Appropriate controls indicate that
I don't have a problem with dirty DNA or bad enzyme or any of the
usual trivial explanations.  Any additional information on
alternative methlation sites will be appreciated.

Brian H. Taylor                         *   Ad hoc loc and
Dept. of Biology, Texas A&M University  *   quid pro quo,
College Station, TX  77843-3258         *   so little time,
                                        *   so much to know!
Phone:  (409) 845-7754                  *
FAX:    (409) 845-2891                  *   Jeremy Hilary Boob
                                        *   (The Nowhere Man)

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