methylation/restriction enzymes

Gary Kucera kucera~gt at
Wed Sep 4 09:44:29 EST 1996

R. Woodward wrote:
> A quick question for someone who has always been puzzled by methylation
> inhibiting restriction enzyme digestion. I believe that the ClaI site
> can be methylated and inhibit cleavage by this enzyme, is this always the case?

No, only when the restriction site is flanked by a G residue 
(i.e. gATCGAT is methylated but cATCGAT is not)

> In a host which does have dam activity are all ClaI sites uncleavable with
> ClaI or only a percentage of the sites?

No, see above

 and finally does XL1Blue strain
> methylate DNA. If the answer to all of these questions is YES how can
> I ClaI digest plasmid DNA which was grown up in XL1Blue cells, or is the
> answer obvious? 

Yes, XL-1 Blue will methylate DNA.

 Thanks for your help
> Robert
> Email  rw200 at
> --

Gary T. Kucera, Scientist
Cellular Sciences/Transgenics Group
GlaxoWellcome Research, Inc.
Five Moore Drive
Research Triangle Park, NC 27709

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