UPDATE: 3/1/13, 12:45 p.m. EST. Information on the names of the lawyers from Latham & Watkins advising Energy Transfer Equity has been added to the ninth paragraph of this story.

Latham & Watkins and a trio of Am Law 200 firms with Lone Star State roots are fueling up on the proposed $1.5 billion cash-and-stock sale of Southern Union Gathering to Regency Energy Partners.