DNA-dependent RNA polymerase requires which cofactor?
Catalysis in RNA polymerase active center depends on two divalent magnesium ions coordinated by invariant aspartate triad DFDGD motif in β' subunit and additional aspartates in β subunit. Metal A lowers pKa of RNA 3' hydroxyl activating it for nucleophilic attack on alpha-phosphate of incoming NTP, while Metal B neutralizes developing negative charge and facilitates pyrophosphate leaving group departure. Chelators like EDTA stripping Mg2+ abolish polymerization. Substituting calcium fails to support chemistry due to geometry differences. Thus Mg2+ is universal essential cofactor for both bacte
Ref: Berg Biochemistry 9th ed. Section 28.1: Mg2+ cofactor two-metal mechanism RNA polymerase; Alberts Chapter 6 Catalytic aspartates
