Science-ing it up like ne'r before

On 24-Jan-08, at 12:55 PM, claire tuttle wrote:

Hello professor. I have a question regarding some things we talked about today (Jan. 24) and the textbook.

In chapter 14 the book talks about methylated base repair, but it says that "mismatched repair in eukaryotes is not based on a methylation signal....researchers have not been able to determine how the eukaryotic enzymes recognize the newly synthesized strand versus the original strand." It then goes on to talk about excision repair in humans, however. So I don't understand how excision repair is really any different for methylation in knowing that bases are mismatched and subsequently having enzymes fix the bases. Can you shed some light on this?

Thanks,
Claire Tuttle (92641075)

Good for you. I should be more careful. Most work on the molecular machinery working with DNA is developed first using bacterial models. THen they try to extend these findings to eukaryotes and often, people like me, teaching the material fail to distinguish cases where what occurs in bacteria does not actually work for eukaryotes. They know there is some sort of repair system but the signal whereby the system recognized the new vs the template strand is unknown. Also it isnt completely clear that methylation is not in any way involved in eukaryotic mismatch repair---there is some in vitro (iei in a test tube) work that suggests it may be involved but the story is not simple. In eukaryotes DNA is methylated (typically at the cytosine residue) and although the full significance isnt understood, it seems to be involved in maintaining a particular developmental state---so it is important say in keeping a muscle cell as a muscle cell or a nerve cell as a nerve cell. Presumably it determines in some way which genes get transcribed in the differentiated cell. Mutants of the gene that methylates (methyltransferases) are usually lethal which would suggest an important role, whatever that may be.

I will try to remember to bring your question up in class on Tuesday.

Martin

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I just thought that was a post-worthy erudite exchange. It is even more hilarious for me that I call him "professor" because he looks exactly, exactly, exactly like Dumbledore. So it's all pretty Potterish, which is always a good thing.