UBS AG probably sold 25 billion Swiss francs ($24 billion) of holdings backed by Alt-A mortgages in a ``fire sale,'' JPMorgan Chase & Co. said, raising its estimate of credit writedowns to 18.5 billion francs. Europe's biggest bank by assets fell as much as 4.2 percent in Swiss trading after JPMorgan analyst Kian Abouhossein widened his estimate of losses from 15 billion francs. The company will likely not pay a dividend this year amid slumping valuations on investments infected by the U.S. home-loan crisis, he said. ``It is highly likely that UBS sold its 25 billion-franc face value prime Alt-A portfolio in a fire sale,'' Abouhossein wrote in the note, dated March 5. ``We believe UBS would be willing to aggressively reduce structured credit assets to clean up the book.'' UBS marked down $19 billion last year, posting the first annual loss since the Zurich-based bank was created in 1998. Merrill Lynch & Co. also raised its estimate for additional charges for UBS today to $21 billion. Valuations for AAA rated securities backed by Alt-A loans, deemed between prime and subprime in expected defaults, slumped as much as 15 percent last month, U.S. lender Thornburg Mortgage Inc. has said. The Swiss bank traded down 3.4 percent at 31.14 francs as of 9:30 a.m. The company has declined 56 percent in the past 12 months, giving it a market value of 64.5 billion francs. ``UBS has set a new strategic direction with the asset fire sale, following a period of mainly orderly asset sales within the global banking system,'' Abouhossein wrote, lowering his share-price estimate by 1 franc to 55 francs. ``UBS actions have led to a spilling over into credit-market prices.'' http://www.bloomberg.com/apps/news?pid=20601087&sid=acNB1dIF9g_g&refer=home Marcel Opsel shall step down immediately from his chairman post....