The board of trustees shall consist of the state treasurer, the commissioner of administration, two members of the senate appointed by the president pro tem of the senate, two members of the house of representatives appointed by the speaker of the house, two members appointed by the governor, and three members who are members of the system, one of whom shall be a retiree elected by a plurality vote of retired members and two of whom shall be employees, elected by a plurality vote of the members of the system not retired for four-year terms. The board so constituted shall determine the procedures for nomination and election of the elective board members. The first two trustees designated above shall serve as trustees during their respective terms of office; the legislative members shall serve as trustees until such time as they resign, are no longer members of the general assembly, or are replaced by new appointments; and the members appointed by the governor shall serve as trustees until such time as they resign or are replaced by new appointments. Any vacancies occurring in the office of trustees shall be filled in the same manner as the office was filled previously except that vacancies occurring in the offices of the elected board members may be filled by the board of trustees until the next regularly scheduled election.