Novel dimerization fold of RAP30/RAP74 in human TFIIF at 1.7 A resolution.

General transcription factor IIF (TFIIF) is required for transcription by RNA polymerase II; it consists minimally of a heterodimer of RNA polymerase-associated proteins RAP30 and RAP74. According to solution and mutagenesis studies, the multiple domains of RAP30 and RAP74 bind PolII, TFIIB, TAF250 and DNA in interactions that are essential for transcription initiation and elongation. The X-ray structure of the RAP30/RAP74 interaction domains at 1.7 A resolution reveals a novel "triple barrel" dimerization fold and suggests with mutant data that interactions with the transcription apparatus are mediated not only by this tripartite beta-barrel, but also via flexible loops and alpha and beta-structures extending from it.