Except as hereinafter provided, the effective date of a registration statement shall be the twentieth day after the filing thereof or such earlier date as the Commission may determine, having due regard to the adequacy of the information respecting the issuer theretofore available to the public, to the facility with which the nature of the securities to be registered, their relationship to the capital structure of the issuer and the rights of holders thereof can be understood, and to the public interest and the protection of investors. If any amendment to any such statement is filed prior to the effective date of such statement, the registration statement shall be deemed to have been filed when such amendment was filed; except that an amendment filed with the consent of the Commission, prior to the effective date of the registration statement, or filed pursuant to an order of the Commission, shall be treated as a part of the registration statement.