Shares of Mercantile Bancorp. rose 6.5% Wednesday on rumors the $34.6 billion-asset St. Louis banking company would sell.

Dow Jones said Bank One Corp., Chicago, was the most likely buyer but a top official at Bank One and a source close to Mercantile denied it. Fueling the rumors was unusually heavy trading activity in Mercantile's stock. About 1.5 million shares were traded Wednesday, and more than 6.3 million on Monday. Mercantile's daily trading average is 354,000 shares.

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