Illustration of RNA polymerase II in action in yeast. RNA (ribonucleic acid) polymerase II (orange) functions in the nucleus in the process of transcription. It unwinds the DNA (deoxyribonucleic acid) double helix (violet), and uses its nucleotide sequence as a template to produce a strand of complementary messenger ribonucleic acid (mRNA, red). RNA polymerase II recognises a start sign on the DNA strand and then moves along the strand building the mRNA until it reaches a termination signal. This single-stranded mRNA will subsequently be translated in the cytoplasm to produce a particular protein.