RNA Polymerase

RNA Polymerase makes RNA from DNA. This protein is the transcriber of messages from the nucleus to the ribosomes in the cytoplasm, to tell them what proteins to make! This particular one is a tiny example from the T7 bacteriophage! It's tiny because it has to fit in a virus. "Normal" polymerases, like the kind found in your cells, are 10-20x bigger, and made of many many cofactors and regualatory proteins. The fact is that viruses care less about the quality of RNA they produce than do human cells. It's part of the reason why viruses mutate so fast.

from 1MSW on pdb