INTERSTATE POWER AND LIGHT COMPANY (an Iowa corporation) 5.100% SERIES D CUMULATIVE PERPETUAL PREFERRED STOCK (Liquidation Amount $25 Per Share) UNDERWRITING AGREEMENT Dated: March 14, 2013Underwriting Agreement • March 20th, 2013 • Interstate Power & Light Co • Electric & other services combined • New York
Interstate Power and Light Company, an Iowa corporation (the “Company”), confirms its agreement (the “Agreement”) with Barclays Capital Inc. (“Barclays”), J.P. Morgan Securities LLC (“J.P. Morgan”), Robert W. Baird & Co. Incorporated (“Baird”) and Wells Fargo Securities, LLC (“Wells Fargo Securities”), and each of the other underwriters named on Schedule A hereto (collectively, the “Underwriters”, which term shall also include any underwriter substituted as hereinafter provided in Section 10 hereof), for whom Barclays, J.P. Morgan, Baird and Wells Fargo Securities are acting as representatives (in such capacity, the “Representatives”), with respect to the issue and sale by the Company and the purchase by the Underwriters, acting severally and not jointly, of the respective principal amounts set forth on Schedule A of 8,000,000 shares of the Company’s 5.100% Series D Cumulative Perpetual Preferred Stock, par value $0.01 per share, with a liquidation preference of $25 per share (the “Sec
