Heterotetramer of two alpha and two beta subunits. The ST- strain is deficient in phototaxis. It is not known if this is due to defective adenylate cyclase activity or defective BLUF domains in this protein. In wild-type E.gracilis, photoactivated adenylate cyclase is found in the paraxonemal bodies (PABs). PABs are absent from this strain. Belongs to the adenylyl cyclase class-4/guanylyl cyclase family.