An apparatus for operating on tissue comprises a body, a lever, an end effector, and a tissue severing assembly. The end effector has a pair of jaws configured to open and close on tissue. The end effector is also capable of delivering RF energy to the tissue. The lever is configured to drive the pair of jaws. The tissue severing assembly comprises a trigger having at least one elongate member, at least one gear, and a firing beam. The trigger may also comprise a button operable to activate the RF energy. The firing beam is operable to sever tissue captured between the jaws. The at least one elongate member, at least one gear, and firing beam are associated such that longitudinal movement of the trigger in a first direction causes longitudinal movement of the firing beam in a second direction.