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Question on restriction/methylate reaction

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#1 lucilius



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Posted 12 November 2009 - 10:08 AM


I have the following question that I can not solve: Some BamHI restriction sites in a particual DNA fragment are no longer cleaved when the DNA is pretreated with M.MspI . What percentage of possible BamHI sites is no longer sensitive for BamHI restriction (pseudostatistically)?
With: M.MspI C*CGG and BamHI G/GATCC

I have no clue how to solve this.

I know that the changes are 1/16 that you have a BamHI restriction site that has 2 GG after the 2 CC at the end.

But then what?

I would think that you have 1/16 change that there are 2 GG's behind the 2 C's and that the change that 1 or 2 of those C are methylated is 3 out of 4 (either first C methylated or second C methylated or both methylated or none of the 2 methylated and this last option is the only one that will still be cut by the BamHI, so in 3 out of 4 it will not cut).

So I would end up saying 1/16 that you have 2 G's behind the 2 C's and then 3/4 that it doesnt cut, making it 3/64 and then I would multiply it by 2 because it doenst matter whetter its the 5'-3' or 3'-5' DNA fragment making it 3/32 in the end.
But is this correct?

Anyone an idea?

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