The Lionstone Group, a Texas-based real estate investment firm, with the financial backing of the Teacher Retirement System of Texas (TRS), closed on the purchase of 11, single-story buildings in the Keystone Technology Park totaling 806,157 square feet. Although the price was undisclosed, Lionstone said the Durham office and life science portfolio is the largest acquisition it has made to-date in its $250 million equity venture with TRS.