Arikay

Hello,

On another forum someone said that, DNA polymerase prevents Genetic mutations.
As I don't know much about it, I was curious if it was true, and how does it effect evolution, if at all?

Thanks,
Ari

scigirl

Different DNA polymerases have different "error correction" mechanisms. They recognize "bumps" in the DNA where bases aren't matched properly, and go back and fix their mistake. Other error correction mechanisms exist as well. But no DNA polymerase can copy DNA perfectly every single time.

scigirl

RufusAtticus

DNA Polymerase has an error correcting function. It can correct its own mistakes. Without the error correcting subunit it incorporates a wrong nucleotide 1 out of every 1,000,000 bases it copies. With the error correcting subunit, 999 out of a thousand wrong nucleotides are fixed and thus the total error rate is reduced to 1 out of every 1,000,000,000 bases copied. (Note these numbers are pulled from memory. I do not guarentee their accuracy.) I believe that this other person is being confused by its specific error-correcting function.

faust

Scigirl and Ruffus answered the question pretty well, but i'd like to add some things. mutations can be caused by things other than copying errors, such as Thymine-dimers, strand breaking, and all kinds of misreads. The error-correcting properties of polymerase also vary by species. Some common polymerases are pretty good. Some are exceptional, like some archaea versions with outstanding error-correcting ability.
Remember though, that mutations can be introduced in a number of ways, even while the double helix is in formation. There are other histones around that function to fix these mutations but they aren't perfect either. If a mutation happens in an area that isnt' being "read" then of course the polymerases won't fix it.

theyeti

To be a bit more direct, the answer to the first question is "yes". The answer to the second question is: It affects evolution by affecting mutation rates. Lowering the mutation rate will generally slow evolution, but as functional genomes grow larger (and replication times grow longer), they're more likely to go into error catastrophe if their mutation rate is too high. Nevertheless, the observed mutation rates are more than enough to account for the genetic differences between living species. But DNA polymerase has likely coevolved with the genomes in which it resides to have a higher fidelity as the functional genome length has increased. In fact, it's conceivable that this is a prerequisite for having larger genomes, and that rare occasions when the right polymerase comes along account for some major bursts of phyletic change.

theyeti

Wounded King

Do histones do anything active in terms of repair Faust? I thought it was more various histone associated proteins.

MortalWombat

Not all DNA polymerases contain proofreading activity. Reverse transcriptases from retroviruses for example do not have it, which is why for instance HIV has such a high mutation rate and is able to readily become resistant to various anti-HIV drugs.

While I'm not aware of any intrinsic DNA repair activities by histones, histone proteins are involved in DNA repair by recruitment of other proteins to the nucleosome. For instance, phosphorylation of Histone H2A in response to DNA damage is thought to alter chromatin structure to allow DNA repair to occur.

In addition, histone acetyltransferase complexes (proteins which regulate chromatin structure by adding acetyl groups to histone proteins) have also been shown to contain DNA repair activity.