Allison was tapped to lead Fannie Mae when the GSE was put into conservatorship in September. Since then the agency has undergone additional internal shifts, including this most recent appointment. Johnson is leaving Hartford Financial Services Group--where he was EVP and CFO--to join Fannie Mae. Before that, he was the CFO at Cendant Corp. and served for 12 years at Merrill Lynch in investment banking.

Allison says, in a prepared statement, "With his broad and deep financial services and capital markets experience, David will help lead Fannie Mae as we assist the market during this unprecedented correction and weather the challenges facing all financial companies today."

The appointment signals that Fannie Mae is settling into a post-conservatorship regime. Allison had been taking on at least some of the responsibilities of CFO; Johnson, the agency says in its press release, will be assuming broad responsibilities as he takes over as CFO.

Hisey joined Fannie Mae in January 2005 as senior vice president and controller, taking on many of the CFO's responsibilities when it went into conservatorship. "Through this period of great change, David [Hisey] has been a rock--for the front office, the financial team and the company--and we appreciate his leadership of our financial team," Allison says.