EX-4.2



 Exhibit 4.2 

Executed in 25 Counterparts, No. 16. 

SUPPLEMENTAL INDENTURE 
 DATED
APRIL 1, 2018 
 UNION ELECTRIC COMPANY 

TO 
 THE BANK OF NEW YORK MELLON,

 AS TRUSTEE 
  

 
 (SUPPLEMENTAL TO
THE INDENTURE OF MORTGAGE AND DEED OF TRUST DATED JUNE 15, 1937, AS AMENDED, EXECUTED BY UNION ELECTRIC COMPANY TO THE BANK OF NEW YORK MELLON, AS TRUSTEE) 
  

 
 4.000% First
Mortgage Bonds due 2048 
 This instrument was prepared by Gregory L. Nelson, Esq., Senior Vice President, General Counsel and Secretary
of Union Electric Company, 1901 Chouteau Avenue, St. Louis, Missouri 63103, (314) 621-3222. 
 WHEN RECORDED
MAIL TO: 
 Craig W. Stensland 
 Union Electric Company 

1901 Chouteau Avenue 
 St. Louis, MO 63103 







 SUPPLEMENTAL INDENTURE, dated the 1st day of April, Two thousand and eighteen
(2018) made by and between UNION ELECTRIC COMPANY, a corporation organized and existing under the laws of the State of Missouri (hereinafter called the “Company”), party of the first part, and THE BANK OF NEW YORK MELLON, formerly The
Bank of New York (successor trustee to Bank of America, National Association, formerly Boatmen’s Trust Company), a bank existing under the laws of the State of New York (hereinafter called the “Trustee”), as Trustee under the
Indenture of Mortgage and Deed of Trust dated June 15, 1937, hereinafter mentioned, party of the second part: 
 WHEREAS, the
Company has heretofore executed and delivered to the Trustee its Indenture of Mortgage and Deed of Trust, dated June 15, 1937, as amended May 1, 1941, April 1, 1971, February 1, 1974, July 7, 1980, February 1, 2000,
August 15, 2002 and May 15, 2012 (said Indenture of Mortgage and Deed of Trust as so amended, being hereinafter referred to as the “Original Indenture”), to secure the payment of the principal of and the interest (and premium, if
any) on all bonds at any time issued and outstanding thereunder, and indentures supplemental thereto dated June 15, 1937, May 1, 1941, March 17, 1942, April 13, 1945, April 27, 1945, October 1, 1945, April 11,
1947, April 13, 1949, September 13, 1950, December 1, 1950, September 20, 1951, May 1, 1952, March 1, 1954, May 1, 1955, August 31, 1955, April 1, 1956, July 1, 1956, August 1, 1957,
February 1, 1958, March 1, 1958, November 5, 1958, March 16, 1959, June 24, 1959, December 11, 1959, August 17, 1960, September 1, 1960, October 24, 1960, June 30, 1961, July 1, 1961,
August 9, 1962, September 30, 1963, November 1, 1963, March 12, 1965, April 1, 1965, April 14, 1966, May 1, 1966, February 17, 1967, March 1, 1967, February 19, 1968, March 15, 1968,
August 21, 1968, April 7, 1969, May 1, 1969, September 12, 1969, October 1, 1969, March 26, 1970, April 1, 1970, June 12, 1970, January 1, 1971, April 1, 1971, September 15, 1971,
December 3, 1973, February 1, 1974, April 25, 1974, February 3, 1975, March 1, 1975, June 11, 1975, May 12, 1976, August 16, 1976, April 26, 1977, October 15, 1977, November 7, 1977,
December 1, 1977, August 1, 1978, October 12, 1979, November 1, 1979, July 7, 1980, August 1, 1980, August 20, 1980, February 1, 1981, October 8, 1981, August 27, 1982, September 1, 1982,
December 15, 1982, March 1, 1983, June 21, 1984, December 12, 1984, June 11, 1985, March 1, 1986, May 1, 1986, May 1, 1990, December 1, 1991, December 4, 1991, January 1, 1992,
September 30, 1992, October 1, 1992, December 1, 1992, February 1, 1993, February 18, 1993, May 1, 1993, August 1, 1993, October 1, 1993, January 1, 1994, February 1, 2000, August 15, 2002,
March 5, 2003, April 1, 2003, July 15, 2003, October 1, 2003, February 1, 2004 (eight separate indentures supplemental thereto), May 1, 2004, September 1, 2004, January 1, 2005, July 1, 2005,
December 1, 2005, June 1, 2007, April 1, 2008, June 1, 2008, March 1, 2009, September 1, 2012, April 1, 2014, March 15, 2015 and June 1, 2017 respectively, have heretofore been entered into between the
Company and the Trustee; and 
 WHEREAS, the following Bonds have heretofore been issued by the Company under the Original Indenture
and remain outstanding: 
 (1) $44,000,000 principal amount of First Mortgage Bonds, Environmental Improvement
Series 1993, which are described in the Supplemental Indenture dated October 1, 1993, $5,000 of which are outstanding at the date of the execution hereof; 

(2) $184,000,000 principal amount of First Mortgage Bonds, Senior Notes Series BB, which are described in the Supplemental
Indenture dated March 5, 2003, all of which are outstanding at the date of the execution hereof; 
 (3) $200,000,000
principal amount of First Mortgage Bonds, Senior Notes Series DD, which are described in the Supplemental Indenture dated July 15, 2003, $198,657,000 of which are outstanding at the date of the execution hereof; 

(4) $60,000,000 principal amount of First Mortgage Bonds, Environmental Improvement Series 2004A (1998A Bonds), which are
described in the Supplemental Indenture dated February 1, 2004, all of which are outstanding at the date of the execution hereof; 

(5) $50,000,000 principal amount of First Mortgage Bonds, Environmental Improvement Series 2004B (1998B Bonds), which are
described in the Supplemental Indenture dated February 1, 2004, all of which are outstanding at the date of the execution hereof; 







 (6) $50,000,000 principal amount of First Mortgage Bonds, Environmental
Improvement Series 2004C (1998C Bonds), which are described in the Supplemental Indenture dated February 1, 2004, all of which are outstanding at the date of the execution hereof; 

(7) $47,500,000 principal amount of First Mortgage Bonds, Environmental Improvement Series 2004H (1992 Bonds), which are
described in the Supplemental Indenture dated February 1, 2004, all of which are outstanding at the date of the execution hereof; 

(8) $300,000,000 principal amount of First Mortgage Bonds, Senior Notes Series GG, which are described in the Supplemental
Indenture dated September 1, 2004, $244,311,000 of which are outstanding at the date of the execution hereof; 
 (9)
$85,000,000 principal amount of First Mortgage Bonds, Senior Notes Series HH, which are described in the Supplemental Indenture dated January 1, 2005, all of which are outstanding at the date of the execution hereof; 

(10) $300,000,000 principal amount of First Mortgage Bonds, Senior Notes Series II, which are described in the
Supplemental Indenture dated July 1, 2005, all of which are outstanding at the date of the execution hereof; 
 (11)
$450,000,000 principal amount of First Mortgage Bonds, Senior Notes, Series MM, which are described in the Supplemental Indenture dated June 1, 2008, $329,283,000 of which are outstanding at the date of the execution hereof; 

(12) $350,000,000 principal amount of First Mortgage Bonds, Senior Notes, Series NN, which are described in the
Supplemental Indenture dated March 1, 2009, all of which are outstanding at the date of the execution hereof; 
 (13)
$485,000,000 principal amount of First Mortgage Bonds, Senior Notes, Series OO, which are described in the Supplemental Indenture dated September 1, 2012, all of which are outstanding at the date of the execution hereof; 

(14) $350,000,000 principal amount of First Mortgage Bonds, Senior Notes, Series PP, which are described in the
Supplemental Indenture dated April 1, 2014, all of which are outstanding at the date of the execution hereof; 
 (15)
$400,000,000 principal amount of First Mortgage Bonds, Senior Notes, Series QQ, which are described in the Supplemental Indenture dated March 15, 2015, all of which are outstanding at the date of the execution hereof; and 

(16) $400,000,000 principal amount of First Mortgage Bonds, Senior Notes, Series RR, which are described in the
Supplemental Indenture dated June 1, 2017, all of which are outstanding at the date of the execution hereof; and 
 WHEREAS, the
Company on August 31, 1955 acquired all of the properties of Union Electric Power Company, the Subsidiary as defined in Article I of the Original Indenture, upon the dissolution of the Subsidiary; the Company, by Supplemental Indenture
dated August 31, 1955, conveyed all of the properties so acquired (other than property of the character defined as excepted property in the granting clauses of the Original Indenture) to the Trustee upon the terms and trusts in the Original
Indenture and the indentures supplemental thereto set forth for the equal and proportionate benefit and security of all present and future holders of the Bonds and coupons issued and to be issued thereunder, all the shares of stock of the Subsidiary
were released from the lien of the Original Indenture; and the Company became entitled to change the general designation of the Bonds so as to omit the words “and Collateral Trust”; and 

  
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 WHEREAS, the Articles of Incorporation of the Company were duly amended on April 23,
1956, to change its corporate name from “Union Electric Company of Missouri” to “Union Electric Company”; and 

WHEREAS, the Articles of Agreement of the Trustee were duly amended effective on January 4, 1982 to change its corporate name from
“St. Louis Union Trust Company” to “Centerre Trust Company of St. Louis”, and further amended on December 9, 1988, to change its corporate name from “Centerre Trust Company of St. Louis” to “Boatmen’s
Trust Company”; and 
 WHEREAS, that on March 13, 1998, Boatmen’s Trust Company merged into NationsBank, National
Association and effective July 5, 1999, changed its name to Bank of America, National Association; and 
 WHEREAS, that on
February 1, 2000, The Bank of New York, as transferee of the corporate trust business of Bank of America, National Association (formerly known as Boatmen’s Trust Company), Trustee under the Original Indenture, became successor Trustee
under the Original Indenture; and 
 WHEREAS, that effective as of July 1, 2008, The Bank of New York changed its name to The
Bank of New York Mellon; and 
 WHEREAS, the Company is entitled at this time to have authenticated and delivered additional Bonds on
the basis of “property additions” upon compliance with and pursuant to the provisions of Section 4 of Article III of the Original Indenture or on the basis of “refundable Bonds” upon compliance with and pursuant to the
provisions of Section 5 of Article III of the Original Indenture; and 
 WHEREAS, the Company desires by this Supplemental
Indenture to provide for the creation of a new series of Bonds under the Original Indenture, to have the designation provided in Article I, Section 1 hereof (herein called the “New Bonds”), and the Original Indenture provides
that certain terms and provisions, as determined by the Board of Directors of the Company, of the Bonds of any particular series may be expressed in and provided by the execution of an appropriate supplemental indenture; and 

WHEREAS, the Original Indenture provides that the Company and the Trustee may enter into indentures supplemental to the Original
Indenture specifically to convey, transfer and assign to the Trustee and to subject to the lien of the Original Indenture additional properties acquired by the Company; and 

WHEREAS, the Company, in the exercise of the powers and authority conferred upon and reserved to it under the provisions of the
Original Indenture and pursuant to appropriate resolutions of the Board of Directors, has duly resolved and determined to make, execute and deliver to the Trustee a Supplemental Indenture in the form hereof for the purposes herein provided; and 

WHEREAS, all conditions and requirements necessary to make this Supplemental Indenture a valid, binding and legal instrument have been
done, performed and fulfilled and the execution and delivery hereof have been in all respects duly authorized; 
 NOW, THEREFORE, THIS
INDENTURE WITNESSETH: 
 That, in consideration of the premises and of the mutual covenants herein contained and of the acceptance of
this trust by the Trustee and of the sum of One Dollar duly paid by the Trustee to the Company at or before the time of the execution of this Supplemental Indenture, and of other valuable considerations, the receipt whereof is hereby acknowledged,
and in order further to secure the payment of the principal of and interest (and premium, if any) on all Bonds at any time issued and outstanding under the Original Indenture, according to their tenor and effect, the Company has executed and
delivered this Supplemental Indenture and has granted, bargained, sold, warranted, aliened, remised, released, conveyed, assigned, transferred, mortgaged, pledged, set over and confirmed and by these presents does grant, bargain, sell, warrant,
alien, remise, release, convey, assign, transfer, mortgage, pledge, set over and confirm unto The Bank of New York Mellon, as Trustee, and to its successors in trust under the Original Indenture forever, all and singular the following described
properties (in addition to all other properties 

  
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heretofore subjected to the lien of the Original Indenture and not heretofore released from the lien thereof)—that is to say: 

FIRST. 
 ALL (except as in
the Original Indenture expressly excepted) power houses, plants, buildings and other structures, dams, dam sites, substations, heating plants, gas works, holders and tanks, together with all and singular the electric, heating, gas and mechanical
appliances appurtenant thereto of every nature whatsoever, now owned by the Company, including all and singular the machinery, engines, boilers, furnaces, generators, dynamos, turbines and motors, and all and every character of mechanical appliance
for generating or producing electricity, steam, gas and other agencies for light, heat, cold, or power or other purposes, and all transmission and distribution systems used for the transmission and distribution of electricity, steam, gas and other
agencies for light, heat, cold or power or any other purpose whatsoever, whether underground or overhead, surface or otherwise, now owned by the Company, including all poles, towers, posts, wires, cables, conduits, manholes, mains, pipes, tubes,
drains, furnaces, switchboards, transformers, conductors, insulators, supports, meters, lamps, fuses, junction boxes, regulator stations, and other electric, steam and gas fixtures and apparatus; all of the aforementioned property being located in
the City of St. Louis, the counties of Adair, Audrain, Benton, Bollinger, Boone, Butler, Caldwell, Callaway, Camden, Cape Girardeau, Clark, Clay, Clinton, Cole, Cooper, Crawford, Daviess, Dunklin, Franklin, Gasconade, Howard, Iron, Jefferson, Knox,
Lewis, Lincoln, Livingston, Macon, Madison, Maries, Marion, Miller, Mississippi, Moniteau, Montgomery, Morgan, New Madrid, Osage, Pemiscot, Perry, Pettis, Phelps, Pike, Pulaski, Ralls, Randolph, Ray, Reynolds, Ripley, St. Charles, St. Francois, Ste.
Genevieve, St. Louis, Saline, Schuyler, Scott, Stoddard, Warren, Washington, and Wayne, Missouri, the counties of Clay, Hancock, Henderson, Madison, Marion, Perry, Piatt and St. Clair, Illinois, and the counties of Des Moines, Henry, Johnson,
Lee, and Washington, Iowa, upon real estate owned by the Company, or occupied by it under rights to so occupy, which real estate is described in, or added through the provisions of, the Indenture of Mortgage and Deed of Trust dated June 15,
1937, the Supplemental Indentures dated May 1, 1941, March 17, 1942, April 13, 1945, April 27, 1945, October 1, 1945, April 11, 1947, April 13, 1949, September 13, 1950, December 1, 1950,
September 20, 1951, May 1, 1952, March 1, 1954, May 1, 1955, August 31, 1955, April 1, 1956, July 1, 1956, August 1, 1957, February 1, 1958, March 1, 1958, November 5, 1958, March 16, 1959,
June 24, 1959, December 11, 1959, August 17, 1960, September 1, 1960, October 24, 1960, June 30, 1961, July 1, 1961, August 9, 1962, September 30, 1963, November 1, 1963, March 12, 1965,
April 1, 1965, April 14, 1966, May 1, 1966, February 17, 1967, March 1, 1967, February 19, 1968, March 15, 1968, August 21, 1968, April 7, 1969, May 1, 1969, September 12, 1969, October 1,
1969, March 26, 1970, April 1, 1970, June 12, 1970, January 1, 1971, April 1, 1971, September 15, 1971, December 3, 1973, February 1, 1974, April 25, 1974, February 3, 1975, March 1, 1975,
June 11, 1975, May 12, 1976, August 16, 1976, April 26, 1977, October 15, 1977, November 7, 1977, December 1, 1977, August 1, 1978, October 12, 1979, November 1, 1979, July 7, 1980,
August 1, 1980, August 20, 1980, February 1, 1981, October 8, 1981, August 27, 1982, September 1, 1982, December 15, 1982, March 1, 1983, June 21, 1984, December 12, 1984, June 11, 1985,
March 1, 1986, May 1, 1986, May 1, 1990, December 1, 1991, December 4, 1991, January 1, 1992, September 30, 1992, October 1, 1992, December 1, 1992, February 1, 1993, February 18, 1993,
May 1, 1993, August 1, 1993, October 1, 1993, January 1, 1994, February 1, 2000, August 15, 2002, March 5, 2003, April 1, 2003, July 15, 2003, October 1, 2003, February 1, 2004 (eight separate
supplemental indentures), May 1, 2004, September 1, 2004, January 1, 2005, July 1, 2005, December 1, 2005, June 1, 2007, April 1, 2008, June 1, 2008, March 1, 2009, May 15, 2012, September 1,
2012, April 1, 2014, March 15, 2015, June 1, 2017 and this Supplemental Indenture, or attached to or connected with such real estate or transmission or distribution systems of the Company leading from or into such real estate. 

SECOND. 
 ALSO,
(except as in the Original Indenture expressly excepted) all franchises and all permits, ordinances, easements, privileges, immunities and licenses, all rights to construct, maintain and operate overhead, surface and underground systems for the
distribution and transmission of electricity, steam, gas or other agencies for the supply to itself or others of light, heat, cold or power, all rights-of-way, all
waters, water rights and flowage rights and all grants and consents, now owned or, subject to the provisions of Article XII of the Original Indenture, which it may hereafter acquire. 

  
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 ALSO, (except as in the Original Indenture expressly excepted) all inventions, patent
rights and licenses of every kind now owned by the Company or, subject to the provisions of Article XII of the Original Indenture, which it may hereafter acquire. 

THIRD. 
 ALSO,
subject to the provisions of Article XII of the Original Indenture, all other property, real, personal and mixed (except as therein or herein expressly excepted) of every nature and kind and wheresoever situated now or hereafter possessed by or
belonging to the Company, or to which it is now, or may at any time hereafter be, in any manner entitled at law or in equity. 

EXPRESSLY EXCEPTING AND EXCLUDING, HOWEVER, from this Supplemental Indenture and from the lien and operation hereof: 

(a) all property expressly excepted and excluded from the Original Indenture, and from the lien and operation thereof; and 

(b) when the amendment set forth in Section 2 of Article III of the Supplemental Indenture dated May 15, 2012 becomes effective, all
Excepted Property as defined in such Section. 
 TO HAVE AND TO HOLD all said properties, real, personal and mixed, mortgaged,
pledged and conveyed by the Company as aforesaid, or intended so to be, unto the Trustee and its successors and assigns forever; 

SUBJECT, HOWEVER, to the exceptions and reservations and matters hereinabove recited, to existing leases, to existing liens upon rights
of way for transmission or distribution line purposes, as defined in Article I of the Original Indenture, and any extensions thereof, and subject to existing easements for streets, alleys, highways, rights-of-way and railroad purposes over, upon and across certain of the property hereinbefore described, and subject also to all the terms, conditions, agreements, covenants, exceptions and reservations
expressed or provided in the deeds or other instruments respectively under and by virtue of which the Company acquired the properties hereinabove described, and to undetermined liens and charges, if any, incidental to construction or other existing
permitted liens as defined in Article I of the Original Indenture; 
 IN TRUST, NEVERTHELESS, upon the terms and trusts in the
Original Indenture and the indentures supplemental thereto, including this Supplemental Indenture, set forth, for the equal and proportionate benefit and security of all present and future holders of the Bonds and coupons issued and to be issued
thereunder, or any of them, without preference of any of said Bonds and coupons of any particular series over the Bonds and coupons of any other series, by reason of priority in the time of the issue, sale or negotiation thereof, or by reason of the
purpose of issue or otherwise howsoever, except as otherwise provided in Section 2 of Article IV of the Original Indenture. 

AND IT IS HEREBY COVENANTED, DECLARED AND AGREED, by and between the parties hereto, for the benefit of those who shall hold the Bonds
and coupons, or any of them to be issued under the Original Indenture, as follows: 
 ARTICLE I 

DESCRIPTION OF THE NEW BONDS 

Section 1. There is hereby created a new series of Bonds to be executed, authenticated and delivered under and secured by the Original
Indenture which shall, subject to the provisions of Section 1 of Article II of the Original Indenture, be designated as “4.000% First Mortgage Bonds due 2048” (the “New Bonds”) of the Company. The New Bonds shall
be executed, authenticated and delivered in accordance with the provisions of, and shall in all respects be subject to all of the terms, conditions and covenants of, the Original Indenture. 

  
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 The New Bonds shall mature on April 1, 2048, and shall bear interest at the rate per annum
set forth in the form of the New Bond contained in Section 3 of this Article I, payable semi-annually in arrears on the 1st day of April and the 1st day of October in each year (each, an “Interest Payment Date”), commencing on
October 1, 2018, and at maturity. The New Bonds shall be payable as to principal and interest in any coin or currency of the United States of America which at the time of payment is legal tender for public and private debts, and shall be
payable, in immediately available funds, at the office of the Trustee. 
 Section 2. The New Bonds will be initially issued in global
form registered in the name of CEDE & CO. (as nominee for The Depository Trust Company). The New Bonds will bear the depository legend in substantially the form set forth in Section 3 of this Article I. Any transfer shall be effected
at the principal office or place of business of the Trustee. The New Bonds are exchangeable for the New Bonds of other denominations, as in the Original Indenture provided, except that payment of a service charge therefor will not be required
by the Company. 
 Notwithstanding the provisions of Section 6 of Article II of the Original Indenture, the New Bonds shall be
dated the date of authentication and shall bear interest from the Interest Payment Date to which interest on the New Bonds has been paid next preceding the date thereof, unless such date is an Interest Payment Date to which interest has been paid,
in which case they shall bear interest from the date thereof, or unless the date thereof is prior to October 1, 2018, in which case they shall bear interest from April 6, 2018; provided, however, that, subject to the provisions of this
Section with respect to failure by the Company to pay any interest on an Interest Payment Date, the holder of any New Bond dated after a record date (as hereinafter defined) for the payment of interest and prior to the date of payment of such
interest shall not be entitled to payment of such interest and shall have no claim against the Company with respect thereto. 
 The person
in whose name any New Bond is registered at the close of business on any record date with respect to any Interest Payment Date shall be entitled to receive the interest payable on such Interest Payment Date notwithstanding the cancellation of such
Bond upon any transfer or exchange thereof subsequent to the record date and prior to such Interest Payment Date, except if and to the extent the Company shall default in the payment of the interest due on such Interest Payment Date, in which case
such defaulted interest shall be paid to the person in whose name such Bond is registered on the date of payment of such defaulted interest or on a subsequent record date for such payment if one shall have been established as hereinafter
provided. A subsequent record date may be established by the Company by notice mailed to the holders of the New Bonds not less than ten days preceding such record date, which record date shall be not more than thirty days prior to the
subsequent Interest Payment Date. The term “record date” as used in this Section with respect to any regular interest payment date shall mean the March 15 or September 15, as the case may be, next preceding such Interest
Payment Date, or, if such March 15 or September 15 shall be a legal holiday in the State of New York or in the State of Missouri or a day on which banking institutions in the Borough of Manhattan, The City of New York, or the City of St.
Louis, Missouri, are authorized by law to close, the next preceding day which shall not be a legal holiday or a day on which such institutions are so authorized to close. 

  
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 Section 3. The New Bonds and the Trustee’s certificate on the New Bonds shall be
substantially in the following forms respectively: 
 [FORM OF FACE OF NEW BOND] 

 

					
	REGISTERED	  		  	REGISTERED

 [DTC Legend 

THIS BOND IS A GLOBAL BOND REGISTERED IN THE NAME OF THE DEPOSITARY (REFERRED TO HEREIN) OR A NOMINEE THEREOF AND, UNLESS AND UNTIL IT IS
EXCHANGED IN WHOLE FOR THE INDIVIDUAL BONDS REPRESENTED HEREBY AS PROVIDED IN THE AMENDED INDENTURE REFERRED TO BELOW, THIS BOND MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY OR BY A NOMINEE OF THE
DEPOSITARY TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY OR BY THE DEPOSITARY OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH SUCCESSOR DEPOSITARY. UNLESS THIS BOND IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE
DEPOSITORY TRUST COMPANY (55 WATER STREET, NEW YORK, NEW YORK), TO THE TRUSTEE FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS REQUESTED BY AN
AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY AND ANY PAYMENT IS MADE TO CEDE & CO., ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL SINCE THE REGISTERED OWNER HEREOF,
CEDE & CO., HAS AN INTEREST HEREIN.] 
 UNION ELECTRIC COMPANY 

(Incorporated under the laws of the State of Missouri) 

4.000% FIRST MORTGAGE BOND DUE 2048 
  

			
	 CUSIP:
 ISIN:
	  	NUMBER:
		
	ORIGINAL ISSUE DATE:                     	  	PRINCIPAL AMOUNT: $                    
		
	INTEREST RATE: 4.000%	  	MATURITY DATE: April 1, 2048

 UNION ELECTRIC COMPANY, a corporation organized and existing under the laws of the State of Missouri
(hereinafter called the “Company”, which term shall include any successor corporation as defined in the Amended Indenture referred to on the reverse hereof), for value received, hereby promises to pay to
                        , or registered assigns, the sum of
                                     Dollars
($                    ), on the Maturity Date set forth above in any coin or currency of the United States of America which at the time of
payment is legal tender for public and private debts, and to pay interest thereon, in like coin or currency, at the Interest Rate set forth above, payable semi-annually in arrears, on April 1 and October 1 in each year (each, an
“Interest Payment Date”) until the Maturity Date, commencing October 1, 2018, and on the Maturity Date or, if the Company shall default in the payment of the principal hereof, until the Company’s obligation with respect to the
payment of such principal shall be discharged as provided in the Amended Indenture referred to on the reverse hereof. Such interest shall be payable from the April 1 or October 1, as the case may be, next preceding the date hereof to which
interest has not been paid, unless the date hereof is an April 1 or October 1 to which interest has been paid, in which case from the date hereof, or unless the date hereof is prior to the first payment of interest, in which case from the
Original Issue Date set forth above. The interest so payable will be paid to the person in whose name this Bond, or the Bond in exchange or substitution for which this Bond shall have been issued, shall have been registered at the close of
business on the March 15 or September 15, as the case may be (each, a “Record Date”), next preceding the date of payment, subject to certain exceptions set forth in the Amended Indenture. The principal of, premium, if any,
and interest on, this Bond are payable, in immediately available funds, at the office of the 

  
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Trustee hereinafter referred to; provided, however, that at the option of the Company, interest on this Bond may be paid by check mailed to the registered holder of this Bond at such
holder’s address as it shall appear on the books of the Company to be kept for that purpose or by a wire transfer to an account designated by the registered holder of this Bond entitled thereto. 

This Bond shall not be entitled to any benefit under the Amended Indenture or any indenture supplemental thereto, or become valid or
obligatory for any purpose, until The Bank of New York Mellon, the Trustee under the Amended Indenture, or a successor trustee thereto under the Amended Indenture, or an agent therefor, shall have signed the form of certificate endorsed hereon. 

The provisions of this Bond are continued on the reverse hereof and such continued provisions shall for all purposes have the same effect as
though fully set forth at this place. 

  
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 IN WITNESS WHEREOF, Union Electric Company has caused this Bond to be signed in its name by its
Chairman of the Board or President or a Vice President by manual signature or a facsimile thereof, and its corporate seal (or a facsimile thereof) to be hereto affixed and attested by its Secretary or an Assistant Secretary by manual signature or a
facsimile thereof. 
 Dated 
  

			
	UNION ELECTRIC COMPANY


 
			
		
	By 	 	 


  

	
	[CORPORATE SEAL]
	
	Attest:
	   

	

 [FORM OF TRUSTEE’S CERTIFICATE] 

This Bond is one of the Bonds, of the series designated therein, described in the within-mentioned Amended Indenture and Supplemental
Indenture of April 1, 2018. 
  

			
	THE BANK OF NEW YORK MELLON, as TRUSTEE
		
	By	 	 
		 	Authorized Officer



  
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 [FORM OF REVERSE OF NEW BOND] 

This Bond is one of a duly authorized issue of Bonds of the Company (herein called the “Bonds”), in unlimited aggregate principal
amount, of the series hereinafter specified, all issued and to be issued under and equally secured by the Indenture of Mortgage and Deed of Trust, dated June 15, 1937, executed by the Company to The Bank of New York Mellon, formerly The Bank of
New York (successor trustee to Bank of America, National Association, formerly Boatmen’s Trust Company), as trustee (herein called the “Trustee”), as amended by indentures supplemental thereto dated May 1, 1941, April 1,
1971, February 1, 1974, July 7, 1980, February 1, 2000, August 15, 2002 and May 15, 2012, between the Company and the Trustee (said mortgage and deed of trust, as so amended, being herein called the “Amended
Indenture”), to which Amended Indenture and all indentures supplemental thereto reference is hereby made for a description of the properties mortgaged and pledged, the nature and extent of the security, the rights of the bearers or registered
owners of the Bonds and of the Trustee in respect thereto, and the terms and conditions upon which the Bonds are, and are to be, secured. To the extent permitted by, and as provided in, the Amended Indenture, modifications or alterations of the
Amended Indenture, or of any indenture supplemental thereto, and of the rights and obligations of the Company and of the holders of the Bonds may be made with the consent of the Company by an affirmative vote of not less than 60% in amount of the
Bonds entitled to vote then outstanding, at a meeting of Bondholders called and held as provided in the Amended Indenture, and by an affirmative vote of not less than 60% in amount of the Bonds of any series entitled to vote then outstanding and
affected by such modification or alteration, in case one or more but less than all of the series of Bonds then outstanding under the Amended Indenture are so affected. Additionally, the Company may amend the Amended Indenture, as supplemented,
by an appropriate written consent of not less than 60% in aggregate principal amount of the Bonds outstanding (and, if the rights of one or more, but less than all, series of Bonds then outstanding are to be affected by action taken pursuant to such
consent, then also by consent of the holders of at least 60% in principal amount of each series of Bonds so to be affected and outstanding hereunder) without a meeting of such Bondholders. No such modification or alteration shall be made which
will affect the terms of payment of the principal of, or interest or premium on, this Bond, which are unconditional. The Bonds may be issued in series, for various principal sums, may mature at different times, may bear interest at different
rates and may otherwise vary as in the Amended Indenture provided. This Bond is one of a series designated as the “4.000% First Mortgage Bonds due 2048” (herein called the “Bonds of this Series”) of the Company, issued under
and secured by the Amended Indenture and described in the indenture (hereinafter called the “New Supplemental Indenture”) dated April 1, 2018, between the Company and the Trustee, supplemental to the Amended Indenture. 

The Bonds of this Series are not entitled to the benefit of any improvement, maintenance or analogous fund. 

All or a portion of the Bonds of this Series may be redeemed at the option of the Company at any time or from time to time. The
redemption price for the Bonds of this Series to be redeemed on any redemption date prior to October 1, 2047 (six months prior to the Maturity Date) will be equal to the greater of the following amounts: (a) 100% of the principal
amount of the Bonds of this Series being redeemed on that redemption date; or (b) the sum of the present values of the remaining scheduled payments of principal and interest on the Bonds of this Series being redeemed on that
redemption date that would be payable if such Bonds matured on October 1, 2047 (six months prior to the Maturity Date) (not including any portion of any payments of interest accrued to the redemption date) discounted to the redemption date
on a semiannual basis (assuming a 360-day year consisting of twelve 30-day months) at the Adjusted Treasury Rate (as defined below); plus 15 basis points, as
determined by the Reference Treasury Dealer (as defined below), plus, in each case, accrued and unpaid interest thereon to the redemption date. The redemption price for the Bonds of this Series to be redeemed on any redemption date on or after
October 1, 2047 (six months prior to the Maturity Date) will be equal to 100% of the principal amount of the Bonds of this Series being redeemed on that redemption date plus accrued and unpaid interest thereon to the redemption date.
Notwithstanding the foregoing, installments of interest on Bonds of this Series that are due and payable on Interest Payment Dates falling on or prior to a redemption date will be payable on the Interest Payment Date to the Holder of this Bond
as of the close of business on the relevant Record Date. 
 With respect to a redemption occurring prior to October 1, 2047
(six months prior to the Maturity Date), the Company shall give the Trustee written notice of the redemption price promptly after the calculation thereof and the Trustee shall not be responsible for such calculation. 

  
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 The Company shall send notice of any redemption at least 10 days but not more than
60 days before the redemption date to each Holder of the Bonds of this Series to be redeemed, and, if less than all Bonds of this Series are to be redeemed, the particular Bonds of this Series to be redeemed will be selected by the Trustee
by lot; provided, that as long as the Bonds of this Series are represented by global certificates, beneficial interests in such global certificates will be selected for redemption by The Depository Trust Company in accordance with its standard
procedures therefor. Unless the Company defaults in payment of the redemption price, on and after the redemption date, interest will cease to accrue on the Bonds of this Series or portions thereof called for redemption. 

Any notice of redemption at the Company’s option may state that such redemption will be conditional upon receipt by the Trustee, on or
prior to the redemption date, of money sufficient to pay the principal of and premium, if any, and interest on, the Bonds of this Series or portions thereof called for redemption, and that if such money has not been so received, such notice will be
of no force and effect and the Company will not be required to redeem such Bonds or portions thereof. 
 “ADJUSTED TREASURY RATE”
means, with respect to any redemption date, the rate per annum equal to the semiannual equivalent yield to maturity of the Comparable Treasury Issue, assuming a price for the Comparable Treasury Issue (expressed as a percentage of its principal
amount) equal to the Comparable Treasury Price for such redemption date. 
 “COMPARABLE TREASURY ISSUE” means the United States
Treasury security selected by the Reference Treasury Dealer as having a maturity comparable to the remaining term of the Bonds of this Series to be redeemed (assuming, for this purpose, that the Bonds matured on October 1, 2047) that would
be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of comparable maturity to the remaining term of such Bonds of this Series. 

“COMPARABLE TREASURY PRICE” means, with respect to any redemption date, (A) the average of the Reference Treasury Dealer
Quotations for such redemption date, after excluding the highest and lowest of such Reference Treasury Dealer Quotations, or (B) if the Company obtains fewer than four such Reference Treasury Dealer Quotations, the average of all such
quotations, or (C) if only one Reference Treasury Dealer Quotation is received, such quotation. 
 “REFERENCE TREASURY
DEALER” means (A) each of Barclays Capital Inc., RBC Capital Markets, LLC, TD Securities (USA) LLC and a Primary Treasury Dealer (as defined below) selected by MUFG Securities Americas Inc., or, in each case, an affiliate thereof, which
are primary U.S. Government securities dealers in the United States (each, a “Primary Treasury Dealer”), and their respective successors; provided, however, that if any of the foregoing shall cease to be a Primary Treasury Dealer, the
Company shall substitute therefor another Primary Treasury Dealer; and (B) any other Primary Treasury Dealer(s) selected by the Company. 

“REFERENCE TREASURY DEALER QUOTATIONS” means, with respect to each Reference Treasury Dealer and any redemption date, the average,
as determined by the Company, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to the Company by such Reference Treasury Dealer at 5:00 p.m. (New
York City time) on the third Business Day preceding such redemption date. 
 In case an event of default, as defined in the Amended
Indenture, shall occur, the principal of all the Bonds at any such time outstanding under the Amended Indenture may be declared or may become due and payable, upon the conditions and in the manner and with the effect provided in the Amended
Indenture. The Amended Indenture provides that such declaration may in certain events be waived by the holders of a majority in principal amount of the Bonds outstanding. 

This Bond is exchangeable by the registered owner hereof, in person or by duly authorized attorney, on the books of the Company to be kept for
that purpose at the office of the Company in the City of St. Louis, Missouri, upon surrender and cancellation of this Bond and on presentation of a duly executed written instrument of transfer, and thereupon a new Bond or Bonds of the same
series, of the same aggregate principal amount and in authorized denominations will be issued to the transferee or transferees in exchange herefor, without payment of any charge other than stamp taxes and other governmental charges incident thereto;
and this Bond with or without others of like series, may in like manner be exchanged for one or more new Bonds of the same series of other authorized denominations but of the same aggregate principal amount; all subject to the terms and conditions
set forth in the Amended Indenture. 

  
 11 








 No recourse shall be had for the payment of the principal of, premium, if any, or the interest
on, this Bond, or for any claim based hereon or on the Amended Indenture or any indenture supplemental thereto, against any incorporator, or against any stockholder, director or officer, past, present or future, of the Company, or of any predecessor
or successor corporation, either directly or through the Company or any such predecessor or successor corporation, whether for amounts unpaid on stock subscriptions or by virtue of any constitution, statute or rule of law, or by the enforcement
of any assessment or penalty or otherwise, all such liability, whether at common law, in equity, by any constitution, statute or otherwise, of incorporators, stockholders, directors or officers being released by every owner hereof by the acceptance
of this Bond and as part of the consideration for the issue hereof, and being likewise released by the terms of the Amended Indenture. 

[END OF FORM OF REVERSE OF NEW BOND] 

Section 4. Until New Bonds in definitive form are ready for delivery, the Company may execute, and upon its request in writing the
Trustee shall authenticate and deliver, in lieu thereof, New Bonds in temporary form, as provided in Section 9 of Article II of the Original Indenture. 

ARTICLE II 
 ISSUE OF THE NEW
BONDS 
 Section 1. The principal amount of the New Bonds which may be authenticated and delivered hereunder is not limited. 

Section 2. The New Bonds in the aggregate principal amount of Four Hundred Twenty Five Million Dollars ($425,000,000), being the initial
issue of the New Bonds, may forthwith at any time or from time to time be executed by the Company and delivered to the Trustee and shall be authenticated by the Trustee and delivered (either before or after the filing or recording hereof) to or upon
the order of the Company, upon compliance by the Company with the applicable provisions of Article III and Article XVIII of the Original Indenture. 

Section 3. After the authentication of the New Bonds, without the consent of any existing Holder of the New Bonds, the Company may
thereafter obtain from time to time the authentication of additional New Bonds pursuant to the terms of the Original Indenture by the order of the Company referring to this Supplemental Indenture having the same terms and conditions as the
Outstanding New Bonds in all respects (including the same CUSIP number), except for the date of original issuance, the offering price and, if applicable, the initial interest accrual date and the initial Interest Payment Date. 

ARTICLE III 
 REDEMPTION OF THE
NEW BONDS AND CONSENT TO AMENDMENTS 
 Section 1. The New Bonds are redeemable as set forth in the form of such Bonds set forth in
Section 3 of Article I hereof. If the Company elects to redeem any New Bonds, it shall notify the Trustee of the redemption date and the principal amount of such Bonds to be redeemed not less than 15 days nor more than 90 days before such
redemption date. 
 Section 2. Each initial and future Holder of the New Bonds, by its acquisition of an interest in such Bonds,
irrevocably (a) consents to the amendments set forth in Article III of the Supplemental Indenture dated as of May 15, 2012, supplemental to the Original Indenture, without any other or further action by any Holder of such bonds, and
(b) designates the Trustee, and its successors, as its proxy with irrevocable instructions to vote and deliver written consents on behalf of such Holder in favor of such amendments at any meeting of Holders, in lieu of any meeting of Holders,
in response to any consent solicitation or otherwise. 

  
 12 








 ARTICLE IV 

COVENANTS 
 The Company
hereby covenants, warrants and agrees; 
 Section 1. That the Company is lawfully seized and possessed of all of the mortgaged property
described in the granting clauses of this Supplemental Indenture to the extent shown on its books and records as of the date hereof; that it has good right and lawful authority to mortgage the same as provided in this Supplemental Indenture; and
that such mortgaged property will be, at the actual date of the issue of the New Bonds, free and clear of any deed of trust, mortgage, lien, charge or encumbrance thereon or affecting the title thereto prior to the lien of the Original Indenture,
except for permitted liens and as set forth in the granting clauses of the Original Indenture and this Supplemental Indenture. 
 ARTICLE V

 THE TRUSTEE 
 The
Trustee hereby accepts the trusts hereby declared and provided, and agrees to perform the same upon the terms and conditions in the Original Indenture and in this Supplemental Indenture set forth, and upon the following terms and conditions: 

The Trustee shall not be responsible in any manner whatsoever for or in respect of the validity or sufficiency of this Supplemental Indenture
or the due execution hereof by the Company or for or in respect of the recitals contained herein, all of which recitals are made by the Company solely. 

ARTICLE VI 
 MISCELLANEOUS
PROVISIONS. 
 Section 1. Except as otherwise defined herein, all terms contained in this Supplemental Indenture shall, for all
purposes thereof, have the meanings given to such terms in Article I of the Original Indenture. 
 Section 2. This Supplemental
Indenture may be simultaneously executed in any number of counterparts, each of which when so executed shall be deemed to be an original; but such counterparts shall together constitute but one and the same instrument. 

  
 13 








 IN WITNESS WHEREOF, said Union Electric Company has caused this Supplemental Indenture to
be executed on its behalf by its Chairman of the Board or President or one of its Vice Presidents and its corporate seal to be hereto affixed and said seal and this Supplemental Indenture to be attested by its Secretary or one of its Assistant
Secretaries; and said The Bank of New York Mellon, in evidence of its acceptance of the trust hereby created, has caused this Supplemental Indenture to be executed on its behalf by its President or one of its Vice Presidents, and its corporate seal
to be hereto affixed and said seal and this Supplemental Indenture to be attested by one of its Vice Presidents, its Secretary, or one of its Assistant Secretaries; all as of the 1st day of April, Two thousand and eighteen. 

 

							
	Attested:	 		 	 UNION ELECTRIC COMPANY,

1901 Chouteau Avenue
 St.
Louis, Missouri 63103

				
	/s/ Craig W. Stensland	 		 	By:  	 	/s/ Ryan J. Martin
	     Craig W. Stensland	 		 	Name: Ryan J. Martin
	     Assistant Secretary	 		 	Title:   Vice President and Treasurer
				
	 Signed, sealed and delivered by

UNION ELECTRIC COMPANY

in the presence of:
	 		 		 	
				
	/s/ Carla J. Flinn	 	  
	 	  
	 	  

	     Carla J. Flinn	 		 		 	
				
	/s/ Lynn M. Smith	 	  
	 	  
	 	  

	     Lynn M. Smith	 		 		 	
	As Witnesses	 		 		 	









							
	Attested:	 		 	THE BANK OF NEW YORK MELLON,
				
	/s/ Arsala Kidwai	 		 	By:  	 	/s/ Francine Kincaid
	     Arsala Kidwai	 		 	Name:    Francine Kincaid
	     Vice President	 		 	               Vice President
				
	 Signed, sealed and delivered by

THE BANK OF NEW YORK MELLON

in the presence of:
	 		 		 	
				
	/s/ Ignazio Tamburello	 	  
	 	  
	 	  

	     Ignazio Tamburello	 		 		 	
				
	/s/ Efren Almazan	 	  
	 	  
	 	  

	     Efren Almazan	 		 		 	
	As Witnesses	 		 		 	









			
	STATE OF MISSOURI	  	}
		  	} SS.:
	CITY OF ST. LOUIS	  	}

 On this 3rd day of April, 2018, before me appeared Ryan
J. Martin and Craig W. Stensland, to me personally known, who, being by me duly sworn, did say that they are the Vice President and Treasurer, and an Assistant Secretary of UNION ELECTRIC COMPANY, a corporation, and that the seal affixed to
the foregoing instrument is the corporate seal of said corporation, and that said instrument was signed and sealed in behalf of said corporation by authority of its Board of Directors, and said Vice President and Treasurer, and Assistant Secretary
acknowledged said instrument to be the free act and deed of said corporation. 
 IN TESTIMONY WHEREOF, I have hereto set my hand and
affixed my official seal at my office, in the City and State aforesaid, the day and year last above written. 
  

					
			
	  
	 		 	/s/ Kelly J. Roth
	 KELLY J. ROTH

Notary Public, Notary Seal
 State of
Missouri
 St. Charles County

Commission # 14440245
 My Commission
Expires May 12, 2018
	 		 	 Kelly J. Roth
 Notary Public

State of Missouri
 St. Charles County

Commission Number: 14440245
 Expires May 12,
2018










			
	STATE OF NEW YORK	  	}
		  	} SS.:
	COUNTY OF NEW YORK	  	}

 On this 29th day of March, 2018, before me appeared
Francine Kincaid, to me personally known, who, being by me duly sworn, did say that she is a Vice President of THE BANK OF NEW YORK MELLON, a corporation, and that the seal affixed to the foregoing instrument is the corporate seal of said
corporation, and that said instrument was signed and sealed in behalf of said corporation, as the trustee thereunder by authority of its Board of Directors, and said Vice President, acknowledged said instrument to be the free act and deed of said
corporation as the trustee under said instrument. 
 IN TESTIMONY WHEREOF, I have hereto set my hand and affixed my official seal at
my office, in the City and State aforesaid, the day and year last above written. 
  

	
	/s/ Bret S. Derman
	      Notary Public
  

	 BRET S. DERMAN

NOTARY PUBLIC STATE OF NEW YORK

KINGS COUNTY
 LIC. # 02DE6196933

COMM. EXP. 11/17/2020