RNA polymerase II and DNA. Animation of the assembling of the units of RNA (ribonucleic acid) polymerase II (orange and yellow). This enzyme functions in the nucleus in the process of transcription. Its function is illustrated at the end of the clip. It unwinds DNA (deoxyribonucleic acid, violet double helix), 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.