UBS CEO Oswald Grübel has dismissed calls for him to resign as politically motivated.  Mr. Gruebel has come under fire after it was discovered that a UBS trader lost $2.3 billion in speculative trades - a scandal he says he's shouldering the blame for.  The pressure on Mr. Gruebel can be attributed, in part, to his pledge to clean up risky business practices - that was given when he came out of retirement to helm the bank.  His plans are to stay in the position until 2013. The bank announced that it has "now covered the risk resulting from the unauthorized trading" and its equities business "is again operating normally within its previously defined risk limits."  Despite that, the fact that the charged acts of fraud date back as far as 2008 has raised questions about the bank's oversight. "The loss resulted from unauthorized speculative trading in various S&P 500, DAX, and EuroStoxx index futures over the last 3 months," UBS said, adding that the magnitude of the bank's risk exposure was hidden by fake trades. Two-Month Window. Mr. Gruebel is expected to survive at least until 11/17/11, when he's scheduled to present to investors an update on the bank's activities. [AP, 9/18/11]