One of the region's biggest real estate investors just plunked down more money into the South of Market neighborhood that will soon give rise to a Alexandria Real Estate Equities - which has specialized in life sciences and now is building offices for Uber in Mission Bay and Stripe in SoMa - will team up on a joint venture with TMG Partners on the already-approved 505 Brannan St. TMG made the announcement Tuesday morning. The investment marks Alexandria's continued expansion into the tech office market speeds past the market for biotechnology lab space.