(A) Schematic representation of THO and Sub2. Recombinant protein fragments that were used for crystallization are indicated by bars. The THO core complex (THO*) contains S. cerevisiae Tho2, Hpr1, Mft1, and Thp2, as well as S. bayanus Tex1 (81% sequence identity with S. cerevisiae Tex1). The DEAD-box ATPase Sub2 contains two recombinase A (RecA)-like domains labeled as Sub2-N and Sub2-C. (B) Coomassie-stained SDS-polyacrylamide gel electrophoresis (PAGE) of purified THO* complex and full-length Sub2. (C) Three views of the THO*•Sub2 complex with THO* in a cartoon representation and Sub2 in a surface representation. (D) Experimental electron density map of Sub2 after density modification, contoured at 1.0σ level corresponding to the view of the upper left panel in C.