Mo. Rev. Stat. § 70.390

Of the commissioners first appointed one shall be appointed to serve for a term of one year, one for two years, one for three years, one for four years and one for five years. At the expiration of the term of each commissioner and of each succeeding commissioner, the governor shall, by and with the advice and consent of the senate, appoint a successor who shall hold office for a term of five years if such successor is appointed to fill a commissioner position described in subsection 1 of this section. If a commissioner is appointed to fill the commissioner position described in subsection 2 of this section, then such commissioner shall hold office for a term of three years. Each commissioner shall hold office until his or her successor has been appointed and qualified.