EXO III deletions

BIOCUKM at osucc.bitnet BIOCUKM at osucc.bitnet
Wed Mar 28 15:00:00 EST 1990

	Sunnie Thompson and I have encountered a problem during
exonuclease III-mediated deletion of a DNA sequence.

	The facts are:
1.  The procedure works well using plasmid DNA vector pGEM3Z as
control, in that increasing times of digestion resulted in ever
smaller DNA products.
2.  Digestion of our target sequence (from cauliflower mosaic
virus DNA) cloned in pGEM3Z proceded for about 400 nucleotides
and then quit.
3.  The quitting point was not precisely the same in all molecules
(several cloned DNAs sequenced).
4.  Increased time or temperature (to 37 deg) failed to increase
the extent of digestion.

	The questions are:
1.  Any hints as to how to overcome this barrier?
2.  Has anyone else had such a problem?  How often?
3.  Are ther any literature reports on this problem?  Where?

	Thanks for any help you can give.

				Ulrich Melcher

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