SAN FRANCISCO (Reuters) - After three years overseeing $7 billion in corporate governance investments at the largest U.S. pension fund, Dennis Johnson said on Thursday he is resigning to manage money for a private fund manager for the Disney family.

Johnson said he is giving up his office as director of corporate governance at Calpers, the $235 billion California Public Employees' Retirement System, to lead Burbank, California-based Shamrock Capital Advisors Inc's Shamrock Activist Value Fund.

Shamrock was formed in the mid-1970s to diversify the stock holdings of the Roy E. Disney family. Its value fund, formed in 2004, invests in publicly traded small-cap companies as an activist stockholder.

Calpers invests through Shamrock's value fund, which also counts other large public pension funds among its investors, and that tie-up led Shamrock's principals to offer Johnson his new job, he said.

"These are individuals who have demonstrated their commitment to constructive, effective shareholder activism," Johnson said. "That's what I'm all about professionally."

"It a tremendous opportunity for me," Johnson added during a telephone interview with Reuters. "If it wasn't, I'd be right here at Calpers."

Shamrock and Calpers will remain partners, with Johnson the link between the two, which share a "very compatible" view on corporate governance, he said.

Calpers routinely presses corporations to improve management on a number of fronts -- the fund keeps a "focus list" of companies it believes are underperformers -- and Shamrock is led by two former board members of The Walt Disney Co (DIS.N: Quote, Profile, Research) who were at the forefront of one of most prominent shareholder fights of the decade.

Roy E. Disney is Shamrock Capital Advisors' chairman and Stanley P. Gold is its president and chief executive. The two helped rally shareholders to force the resignation of former Disney Chief Executive Michael Eisner in 2005.