Commerce Bank (CBH) sank 2% in heavy trading Wednesday after a federal investigation of the bank prompted an analyst downgrade.

CIBC World Markets cut the stock to sector performer from sector outperformer. Analyst Meredith Whitney, who suspended her $43 price target, said "it is simply imprudent to recommend the stock while the company is under its current investigation."

Commerce shares slid 8% Tuesday after the fast-growing Cherry Hill, N.J., bank said it is being probed by the Office of the Comptroller of the Currency and the Board of Governors of the Federal Reserve System for "transactions with its officers, directors and related parties, including transactions involving bank premises."

Shares fell 63 cents early Wednesday to a 52-week low of $31.20.

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