FACTBOX: Key events in subprime fallout at UBS

ZURICH (Reuters) - UBS's subprime trouble worsened on Wednesday when the Swiss-based bank announced a $4 billion hit in yet another round of write-downs, causing hefty fourth-quarter and full-year losses.

UBS -- one of the hardest-hit banks worldwide from the credit crisis -- in an early release of its numbers said its subprime damage now amounted to some $18.4 billion, announcing a full-year loss of 4.4 billion Swiss francs ($4.03 billion).

Following are key events in the world's largest wealth manager's woes, which started last year in May, when it closed down its Dillon Read hedge fund unit.

DILLON READ HEDGE FUND UNIT CLOSED - MAY 3

UBS shocked investors by closing down its Dillon Read hedge fund unit after posting lower-than-expected first-quarter results, a rare event from the bank, whose track record had earned it a reputation as a serial outperformer.

Dillon Read Capital Management -- which UBS set up in 2005 under the helm of star banker John Costas -- had run up losses of 150 million Swiss francs ($136.5 million) in the first quarter. Costas was sidelined as a result.

CHIEF EXECUTIVE WUFFLI LEAVES - JULY 6

Peter Wuffli, its unassuming chief executive, is replaced by his deputy Marcel Rohner.

The reasons for Wuffli's departure are still not clear, although the bank stressed at the time there had been no disagreement over strategy.

But the sudden departure, which the bank said was because Wuffli had been passed over for the position of chairman, seemed to strengthen the position of UBS Chairman Marcel Ospel, who gained another three years at the helm of the bank.

Analysts demanded more transparency about the reasons for the management change, with some doubting Rohner had enough clout to lead one of the world's biggest banks.

WRITE-DOWNS TO CAUSE THIRD-QUARTER LOSS - OCTOBER 1

UBS warned a 4 billion franc subprime hit would cause a third-quarter pre-tax loss of between 600 and 800 million francs.

It also said Rohner would take over the helm at UBS's investment bank from Huw Jenkins for now, UBS said, while Marco Suter would replace Clive Standish as chief financial officer.

A few weeks later, UBS's quarterly loss -- its first in nine years -- at 726 million francs, was within its predicted range.

Just ahead of the earnings, the bank warned of more write-downs.