Any such assistant prosecuting attorney shall hold his office during the pleasure of the prosecuting attorney appointing him, perform any and all duties pertaining to the office of prosecuting attorney at such time or times as he may be required so to do by the prosecuting attorney and during the absence or disability from any cause of the prosecuting attorney, but he shall be subject to all the legal disqualifications and disabilities of the prosecuting attorney, and shall before entering upon the duties of his office, take and subscribe to oath of office prescribed by the constitution of this state and file the same with the county clerk of his county. Any such assistant prosecuting attorney shall be allowed by the county for his services such reasonable compensation as the board of supervisors shall determine.