Divalent cation is required for polymerase activity

 Divalent cations such as magnesium ion form complex with NTP. This property of divalent cation is required for RNA polymerase activity, because the active site of polymerase binds to NTP through these ions. In fact, all experiments using polymerases should contain salts including divalent cations such as MgCl2 or MnCl2, in their reaction mixture. The amount of divalent cation significantly influences to the activity of polymerases. Therefore, we should measure the amount of solution containing MgCl2 or MnCl2 carefully when we add them into the reaction mixture of RNA polymerase.