This is the helical bundle domain (also referred to as the headlock domain) from RNA polymerase I-specific transcription initiation factor Rrn6, a component of a multisubunit transcription factor essential for the initiation of rDNA transcription by Pol I [1,2]. This is a helical domain found towards the C-terminal, adjacent the beta-propeller, that wraps around Rrn7 and is part of module II of the core factor (CF) [2]. The DNA-bound CF resembles a right hand in which the N-terminal regions of both Rrn11 and Rrn6 (the beta-propeller domain) constitutes the palm, the thumb is composed of the C-terminal of Rrn11 and the fingers and knuckles correspond to Rrn7 and the C-terminal half of Rrn6 (this domain), respectively [3].

1: RRN6 and RRN7 encode subunits of a multiprotein complex essential for the initiation of rDNA transcription by RNA polymerase I in Saccharomyces cerevisiae. Keys DA, Vu L, Steffan JS, Dodd JA, Yamamoto RT, Nogi Y, Nomura M; Genes Dev. 1994;8:2349-2362. PMID:7958901

2: Structural Basis of RNA Polymerase I Transcription Initiation. Engel C, Gubbey T, Neyer S, Sainsbury S, Oberthuer C, Baejen C, Bernecky C, Cramer P; Cell. 2017;169:120-131. PMID:28340337

3: Structural mechanism of ATP-independent transcription initiation by RNA polymerase I. Han Y, Yan C, Nguyen THD, Jackobel AJ, Ivanov I, Knutson BA, He Y; Elife. 2017; [Epub ahead of print] PMID:28623663