Following Moody's downgrade of the US sovereign rating last Friday, which triggered a chain reaction, the ratings of major US banks, including Bank of America (BAC.US) and JPMorgan (JPM.US) , were further downgraded on Monday. However, US Treasury yields ebbed from their highs, leading US stocks to open lower and close higher on Monday. The S&P 500 finished up 5 points at 5,963, marking its sixth consecutive day of gains; the DJIA closed up 137 points or 0.3% at 42,792; and the Nasdaq remained stable, ending up 4 points at 19,215.Related NewsCentral Parity of USD/ RMB Adds 25 bps to 7.1938Insurance company UnitedHealth (UNH.US) closed up 8%, shoring up the DJIA, and was the best performer among the 30 DJIA components.Banks deteriorated, with Goldman Sachs (GS.US) and JPMorgan sinking over 1%.(Real-time Streaming US Stocks Quote; Except All OTC quotes are at least 15 minutes delayed.)