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dam-/dcm- bugs and mutations??

Victor Levenson levenson at uic.edu
Thu Feb 20 11:39:58 EST 1997

"Dr. Duncan Clark" <duncan at genesys.demon.co.uk> wrote:

>>I need to cut my construct with BclI and - therefore- have to put it
>>through dam/dcm- strain (DM1, in my case). These bugs do not repair
>>mismatches that occur during DNA replication (I assume that the
>>enzymology of plasmid replication is the same as for the genomic DNA

>If E.coli B which is naturally dcm - was mismatch repair minus it would
>mutate horribly. I'm think you may be mixing up mutS, mutL mutations
>with dam and dcm. I've never seen a report that says dam dcm- strains
>are mismatch repair minus so I wouldn't worry. 

>For Bcl I, you just need dam-. Try JM110 or I think Stratagene have an
>endA derivative. 



Thanks for your post, but... In Gram- starins mismatch repair proteins
Mut HLS recognize the mismatch (I think MutS is the one responsible
for recognition) and then excise mispaired base (MutH endonuclease).
The big question is to choose which strand is the template and which -
the product. A mistake in recognition can lead to fixation of a
mutation instead of repairing it. It is my understanding that
hemimethylated strand is recognized as the template  -  but
methylation requires functional dam/dcm.  If in dam-/dcm- strains
template is chosen at random so that there is a 50/50 chance to either
eliminate or fix a mutation, there should be some record of
substantially increased mutation rate in dam-/dcm- strains. So, if you
happen to come across smthng like that, can you drop me a line?


Victor Levenson MD/PhD
Res Asst Prof
UIC, Dept of Genetics
levenson at uic.edu 

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