NEW YORK - In dramatic developments on the Wall Street, Merrill Lynch, an investment giant, agreed to sell itself to Bank of America for roughly $50 billion to avert a deepening financial crisis, while another prominent securities firm, Lehman Brothers, filed for Chapter 11 bankruptcy protection. The moves mark the latest chapter in a tumultuous year in which once-proud financial institutions have been brought to their knees as a result of tens of billions of dollars in losses because of bad mortgage finance and real estate investments. They culminated a weekend of frantic around-the-clock negotiations, as Wall Street bankers huddled in meetings at the behest of Bush administration officials to try to avoid a downward spiral in the markets stemming from a crisis of confidence, according to media reports. It remains to be seen whether the sale of Merrill, which was worth more than $100 billion during the last year, and the controlled demise of Lehman will be enough to finally turn the tide in the yearlong financial crisis that has crippled Wall Street. The market took a strong turn down Monday, reacting to Lehman's plan to wind down its trading operations. Questions remain whether other companies may still falter, like the American International Group, the large insurer, and Washington Mutual, the nation's largest savings and loan. Both companies' stocks fell precipitously last week. Though the government took control of the troubled mortgage finance companies Fannie Mae and Freddie Mac only a week ago, investors have become increasingly nervous about the difficulties of major financial institutions to recover from their losses. How things play out could affect the broader economy, which has been weakening steadily as the financial crisis has deepened over the last year, with unemployment increasing as the nation's growth rate has slowed, experts said. What will happen to Merrill's 60,000 employees or Lehman's 25,000 employees remains unclear. OIL PRICES Meanwhile, oil prices -- affected by the developments on the Wall Street --tumbled to a seven-month low Monday. Crude's steep decline " prices tumbled as much as $7 over the weekend " also came as early signs suggested that Hurricane Ike delivered less damage than feared to the Gulf Coast energy oil and gas infrastructure. Light, sweet crude for October delivery fell $3.57, or 3.53 percent, to $97.61 a barrel on the New York Mercantile Exchange, after earlier dropping to $94.13, the lowest level since Feb. 14. A close at that level would be oil's first settlement under $100 since March 4.