RNA polymerase II. Molecular model showing the structure of the enzyme RNA polymerase II (blue and white) during transcription. This enzyme synthesises a complementary mRNA (messenger ribonucleic acid) strand (red strand) from a strand of DNA (deoxyribonucleic acid) during a process called transcription. The double stranded DNA molecule (yellow and orange) is at bottom right of the RNA polymerase molecule. The RNA polymerase molecule is using the yellow DNA strand as a template for the mRNA. mRNA is the intermediary between DNA and its protein product.