Membership in the public service commissioners' retirement system provided by §§ 65-151 — 65-168 shall be optional with each commissioner. For the purpose of providing further funds with which to pay the retirement or disability compensation provided for in §§ 65-151 — 65-168, every commissioner who desires to avail himself of the benefits of said sections shall contribute to the public service commissioners' retirement fund an amount annually equal to four per cent (4%) of his gross annual salary as commissioner, such contributions to begin on or after May 7, 1969 or upon the appointment or election and qualification of such commissioner thereafter. This contribution shall be made in equal monthly instalments, which the commissioner of finance and administration shall deduct from the monthly compensation of such commissioner and credit the same to the public service commissioners' retirement fund. Every commissioner in office, on May 7, 1969, who desires to come under the provisions hereof, shall notify the commissioner of finance and administration, by registered or certified return-receipt mail, on or before June 30, 1969. All commissioners elected or appointed after May 7, 1969 shall, within sixty (60) days after such appointment or election and their qualification by virtue of such election or appointment, elect whether or not to come under the provisions of §§ 65-151 — 65-168. Every commissioner electing to come under the provisions of said sections shall continue his contributions to the public service commissioners' retirement fund, as herein provided, as long as he remains in office. Any commissioner in office on May 7, 1969 and who has had prior service, as “service” is defined by § 65-152(b) may, at the time that he notifies the commissioner of finance and administration of his desire to come under the provisions of §§ 65-151 — 65-168, further notify him, in the manner hereinabove prescribed, of his desire to receive credit for such prior service for the purpose of said sections, reciting in his notice the period for which he seeks credit and the nature of his service, i.e., whether as a commissioner, a member of the general assembly or the head of an administrative department of state government, or a combination of any or all of such categories of service, subject to the limitations set forth in § 65-152(b) as to service in the general assembly and/or as the head of an administrative department of state government, and shall remit to the treasurer of the state contributions at the rate of four per cent (4%) of his gross salary or compensation for all such service compensated for prior to May 7, 1969, together with interest thereon at the rate of six per cent (6%) per annum. Thereupon such commissioner shall be entitled to service credit for such period of prior service.

Provided, however, that any commissioner who is presently a member of any other state retirement system and who elects to come under the provisions of §§ 65-151 — 65-168, shall, as of the date that he notifies the commissioner of finance and administration of such election, cease to be a member of any such other state retirement system and any contributions made by such commissioner to such other state retirement system, with respect to any service performed as an official or employee of the state of Tennessee, whether the same comes within the definition of “service” contained in § 65-152(b) or not, shall, any other provision of this Code to the contrary notwithstanding, be transferred from such other state retirement system to the public service commissioners' retirement system as of the date that the commissioner ceases to become a member of such other system.

Provided, further, that in the event that the sum so transferred from any other state retirement system to the public service commissioners' retirement system, as hereinabove prescribed, with respect to any commissioner electing to come under the provisions of §§ 65-151 — 65-168 shall be equal to or in excess of the amount which such commissioner would be otherwise required to remit to the treasurer of the state in order to establish credit for prior service, as “service” is defined in § 65-152(b), that no further or other payment shall be made by such commissioner in order to establish credit for prior service under the terms of §§ 65-151 — 65-168. In the event that the contributions transferred from any other state retirement system to the public service commissioners' retirement system with respect to any commissioner electing to come within the provisions of said sections and to obtain for prior service, as “service” is defined in § 65-152(b) should not equal the amount which such commissioner would otherwise under the provisions of this section be required to remit to the treasurer of the state in order to establish credit for such prior service then in order to receive credit for such prior service for the purposes of §§ 65-151 — 65-168 such commissioner shall remit to the treasurer of the state an amount equal to the difference between the sum he would otherwise be required to remit had his contributions to any other state retirement system not been transferred to the public service commissioners' retirement system and the amount of his contributions so transferred to the public service commissioners' retirement system.

In the event that contributions transferred from any other state retirement system to the public service commissioners' retirement system with respect to any commissioner who elects to come within the provisions of §§ 65-151 — 65-168 and who seeks to obtain credit for prior service as defined by § 65-152(b) shall exceed the amount which such commissioner shall be required to remit to the treasurer of the state in order to obtain such credit, shall exceed the amount required to be remitted, the excess of the contributions so transferred shall be retained in the public service commissioners' retirement fund for the purposes of §§ 65-151 — 65-168.