. "Adenylyltransferase activity is inhibited by the inhibitory helix present at the N-terminus: Glu-252 binds ATP and competes with ATP-binding at Arg-391, thereby preventing adenylyltransferase activity. Activation dissociates ATP-binding from Glu-252, allowing ordered binding of the entire ATP moiety with the alpha-phosphate in an orientation that is productive for accepting an incoming target hydroxyl side chain (By similarity)." . .