(Reuters) – Japan’s Mizuho Financial Group Inc will acquire independent investment bank Greenhill (NYSE:GHL) & Co Inc in an all-cash transaction, in a bid to expand further into U.S. investment banking.

Mizuho will pay $15 per share of Greenhill in cash, reflecting an enterprise value of about $550 million, including assumed debt, the companies said in a joint statement on Monday.

The deal announcement prompted Greenhill shares to more than double to $14.68 in early hours of trading.

The Greenhill acquisition follows the Japanese lender’s efforts to beef up its overseas businesses. Earlier this year, Mizuho planned to acquire Texas-based private equity placement agent Capstone Partners.

Of Japan’s three megabanks, Mizuho has, however, been slower to move than bigger rivals Mitsubishi UFJ (NYSE:MUFG) Financial Group and Sumitomo Mitsui (NYSE:SMFG) Financial Group.

The Greenhill business will sit within Mizuho’s banking division, led by Michal Katz, head of banking in the Americas, the statement said. Greenhill Chairman and CEO Scott L. Bok will become chairman of the M&A and restructuring advisory business, it added.

Last year, Mizuho CEO Yoshiro Hamamoto told Reuters that the group’s brokerage arm Mizuho Securities Co “has room for further growth” in the United States and acquisitions were an option it was exploring.