Eukaryotic nuclear RNA polymerases (EC 18.104.22.168)
DNA-dependant RNA polymerases (ribonucleoside triphosphate: RNA nucleotidyltransferase, EC22.214.171.124) catalyse the synthesis of RNA from ribonucleoside triphosphates in the presence of a DNA template and divalent cation (1). The RNA molecules are synthesized complementary and antiparallel to one of the DNA strands in a 5 to 3 direction. The ribonucleotides are covalently joined together by internucleoside 3 to 5 phosphodiester bonds with concomitant release of inorganic pyrophosphate. In order for the polymerase to do this, it must “recognise” the beginning of the DNA sequence to be transcribed within the double-stranded template; insert the correct nucleotide residue into each position, as determined by the template sequence; carry out synthesis, so that RNA is synthesized from beginning to end as a consequence of one polymerase binding event; and recognise termination signals in order to end RNA synthesis at the appropriate point.