Troubled Swiss banking giant UBS AG suddenly replaced its chief executive officer yesterday, appointing Oswald Gruebel - former head of rival Credit Suisse Group - to take over immediately. Mr. Gruebel's experience in leading Credit Suisse through a turnaround before he left two years ago will prove invaluable, UBS said. He replaces Marcel Rohner, who has resigned. UBS, one of the pillars of Switzerland's banking industry, has had massive losses related to the U.S. subprime mortgage crisis and is also facing legal pressures in the U.S. over allegations it has helped wealthy Americans evade taxes. Mr. Gruebel, 66, said his top priority will be regaining trust, followed by restoring profitability. UBSN (Zurich) rose 1.64 to 11.74 Swiss francs ($12.64).