The U.S. regulator for Fannie Mae and Freddie Mac accuses the banks of negligence in misrepresenting the risks embedded in the securities sold to the home-finance giants.In the latest government effort to recoup mortgage meltdown losses, the federal regulator for Fannie Mae and Freddie Mac sued 17 banks over mortgage bonds that were sold to the giant home-finance companies during the housing boom and proved to be toxic.