Mizuho Financial Group Inc. will buy U.S. M&A advisory firm Greenhill & Co Inc. for $550 million including debt, the companies said on Monday, as Japan's No. 3 lender eyes a bigger share of the world's largest investment-banking fee pool, Reuters reported. The $15-per-share offer represents a premium of 121% to Greenhill's last closing price. Its shares had dropped nearly 40% over the 12 months till Friday's close as high interest rates weighed on dealmaking activity. Greenhill shares more than doubled to $14.68 on Monday after the announcement, but are still below their 2004 initial public offering price of $20. Mizuho has doubled down on U.S. debt underwriting since its 2015 acquisition of Royal Bank of Scotland's North American corporate loan portfolio, leaving M&A advisory and equity underwriting as areas targeted for further growth. Last year, it bought Texas-based private equity placement agent Capstone Partners. Other Japanese banks have also been expanding their foothold in the U.S. The Greenhill business will sit within Mizuho's banking division, led by Michal Katz, head of banking in the Americas. Yoshiro Hamamoto, CEO of Mizuho's brokerage arm, last year told Reuters that the group "has room for further growth" in the United States, and that acquisitions were an option it was exploring. Read more.