Atlanta and Cleveland are far from Wall Street, but regional banks in those and other U.S. cities are mimicking their bigger competitors by plunging into capital markets.

SunTrust Banks, KeyCorp and Citizens Financial Group are among large regional lenders that have been building out their investment-banking capabilities as stubbornly low interest rates have crimped profits. Now they're reaping the benefit, reporting record fee income from the units in the first half of the year.

Investment-banking revenues at seven of the 11 largest regional banks that break out results for the business climbed a combined $339 million in the first half of the year. The lenders are offering merger advice, debt underwriting and help raising capital to the same types of middle-market companies that they've long provided with routine banking services. That segment of the market has been eager to grow in recent years, with 31% of executives in a recent SunTrust survey saying they'd like to make a major capital investment over the next five years and 17% interested in acquiring another company.