RNA polymerase. Molecular model of RNA polymerase (beige and pink) transcribing a strand of mRNA (messenger ribonucleic acid, centre) from a DNA (deoxyribonucleic acid) template (pink and purple). This is RNA polymerase I from the Qbeta bacteriophage, a virus that infects Escherichia coli bacteria. mRNA is the intermediary between DNA and its protein product. This enzyme produces mRNA from viral DNA inserted into the bacteria's genome.