PARIS — UBS, the largest Swiss bank, said Tuesday that it would write down another $19 billion related to the American real estate market and said that its chairman, Marcel Ospel, would step down.
UBS said the write-down would result in a first-quarter loss of about 12 billion Swiss francs, or $12 billion, and that it would seek new capital of about $15 billion, the second time it has announced plans to raise money since the credit markets began to contract.
