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Origin DNA melting and unwind in DNA replication Because of the development of structure biochemistry, we come up some different of opinions which are based on different helicases in different cells. We use some biochemical methods to find the function of helicases and the mechanisms of the intiation of the DNA replication. There are two typical models, E1 and LTag. Because they have some differences in their structure, so they do their work in different ways. E1 mechanism: In the E1 hexammer, the six ß-hairpins in the central channel are arranged in a staircase-like structure. Two adjacent E1 trimers assemble ate the origins to melt the origin.Then a ring shaped E1 hexamer is formed around the melted ssDNA to from a fork. Ltag: The channel diameters of these hexamers vary between 13-17 A, and has planar ß-hairpins in the channel. The origin was pumping into the channel, and squeezing by the channel, so it remodeled, and the hydrogen between base pair are broken up. Then when the two subunits go to a relative large chamber, the melting region expanded. At last, the ssDNA go into the Zn-domain. Although, the two mechanism is built up on the structural data base, it still needs more experiments support. As we know, there are really so many kinds of helicases. Now, we are working on the most simple helicases, and try to find the different mechanisms. They have some similarities, such as they all have the hexamer structure. However, they have some differences, either. For they always have some differences in their structures, contribute huge differences in their function and mechanisms.