California Public Employees Retirement System, with $175 billion in assets, and Hines international real estate firm acquired 50 Fremont Center in San Francisco through their joint venture, National Office Partners. The sellers were a partnership of the Fremont Group and Shorenstein. Terms of the deal were not disclosed. The 795,000-square-foot Class A office property in the citys central business district represents the joint ventures ninth and largest acquisition. The ventures portfolio is now valued at more than $1.8 billion.