Sumitomo Bank Ltd. of Japan is seeking a buyer for its California retail banking unit, the Asian Wall Street Journal has reported. The newspaper said Sumitomo Bank has commissioned U.S. investment banking firm Goldman, Sachs & Co. to find a buyer for San Francisco-based Sumitomo Bank of California. Goldman has already approached several California banks to gauge their interest, the newspaper reported. A sale could be worth up to $1 billion, it said. Sumitomo operates 47 retail branches in the state. Bank spokespersons weren't available to comment on the report. Sumitomo Bank of California's shares fell $2.25 to close at $40.63 on Nasdaq trading. The Japanese parent owns 85% of the California unit.