In the third major defection from the country’s top pension fund this year, Dennis Johnson, the corporate governance director for the California Public Employees’ Retirement System (CalPERS) is leaving to join the Shamrock Activist Value Fund. Shamrock, based in Burbank, Calif., has $1 billion in committed capital for investment in public companies.

Johnson, who served in his role for three years, is credited with stepping up CalPERS’ efforts to hold more companies in which it invests to higher accountability standards. This includes an annual “Focus List” program that identifies companies with poor financial performance and corporate governance practices.

In his place, senior investment officer for public equities Eric Baggesen will take over Johnson’s 17-member group until a successor is found.