Initiation of transcription of ribosomal DNA (rDNA) in yeast involves an interaction of upstream activation factor (UAF) with the upstream element of the promoter, to form a stable UAF-template complex. UAF, together with the TATA-binding transcription initiation factor protein TBP, then recruits an essential core factor to the promoter, to form a stable preinitiation complex [1]. This Rrn9 domain, which seems to be constrained to fungi, is the two highly conserved regions of proteins which form one of the subunits of UAF and appears to be the region responsible for the interaction with TBP. The family includes the S.pombe Arc1 protein, Swiss:Q10204, which is found to be essential for the accumulation of condensin at kinetochores [2].

1: Interaction of TATA-binding protein with upstream activation factor is required for activated transcription of ribosomal DNA by RNA polymerase I in Saccharomyces cerevisiae in vivo. Steffan JS, Keys DA, Vu L, Nomura M; Mol Cell Biol. 1998;18:3752-3761. PMID:9632758

2: Dissection of the essential steps for condensin accumulation at kinetochores and rDNAs during fission yeast mitosis. Nakazawa N, Nakamura T, Kokubu A, Ebe M, Nagao K, Yanagida M; J Cell Biol. 2008;180:1115-1131. PMID:18362178