Expression, proteolytic analysis, reconstitution, and crystallization of the τ60/τ91 subcomplex of yeast TFIIIC

The transcription factor IIIC (TFIIIC) is a multisubunit DNA-binding factor required for promoter recognition and TFIIIB assembly on tRNA genes transcribed by RNA polymerase III. Yeast TFIIIC consists of six subunits, organized in the two globular subcomplexes τA and τB, which recognize two internal tDNA promoter elements, the A and the B block, respectively. As a first step toward a detailed structural analysis of TFIIIC, we report here the expression, proteolytic analysis, reconstitution, and crystallization of the complex between yeast TFIIIC subunits τ91 and τ60. Proteolysis provided an insight into the domain structure of τ60 and τ91. Both the proteins form a stable complex that does not require an N-terminal, protease-sensitive extension of τ91. Crystals diffracting beyond 3.2 Å were obtained from a complex formed by full-length τ60 and the N-terminally truncated form of τ91 lacking this extension.