An actuator assembly is for a lock including a handle, a latch, a retractor for retracting the latch when the handle rotates, and a lock member displaceable between locked and unlocked positions, which either releasably couples the handle with the retractor or releasably prevents handle rotation. The actuator includes a motor having a shaft rotatable about an axis and a coupler spring disposed about the axis and having a first end coupled with the lock member and a second end. A drive member is coupled or integrally formed with the motor shaft and has a helical drive surface threadably engaged with the coupler spring second end, such that rotation of the shaft displaces the coupler spring along the axis to move the lock member between the locked and unlocked positions. Preferably, the drive member includes a spring coupled with the motor shaft and threadably engaged with the coupler spring.