Regulatory subunit of a potassium efflux system that confers protection against electrophiles. Required for full activity of KefB. a quinone + H(+) + NADH = a quinol + NAD(+) a quinone + H(+) + NADPH = a quinol + NADP(+) Interacts with KefB. Belongs to the NAD(P)H dehydrogenase (quinone) family. KefG subfamily.