TOKYO (AP): Japan's main stock index has fallen 3.7 percent Monday as the dollar sank to a 12 1/2-year low against the yen.

Investors are also jittery over news that JP Morgan Chase is buying rival investment bank Bear Stearns, which has been battered by its exposure to bets on risky mortgages.

Invesors see the takeover as a sign that the credit crisis problems are deep and not going away.

The Nikkei 225 stock index sank 454 points, or 3.7 percent, to 11,787.51. Earlier, it had fallen as much as 4.5 percent.