Plan Sponsor Use of Affiliated Broker -- Prohibited Transaction?

[Guest Alley]

Plan sponsor wants to switch its brokerage services for its 401(k) plan from an outside brokerage to an affiliated brokerage (either the plan sponsor and the brokerage have a common parent company, or the brokerage is a subsidiary of the plan sponsor -- I'm not sure which and can find out but I don't think it matters). The plan sponsor is informed that others similarly situated in its industry are doing this. I haven't found any applicable exemption to the pohribited transaction rules. Is there any exemption from the prohibited transaction rules for this scenario?