methylation/restriction enzymes

[Gary Kucera]

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 cus.cam.ac.uk
> 
> --

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