This is OB domain found in RPA43 proteins (DNA-directed RNA polymerase I subunit RPA43, also known as A43) in yeast. Functional analysis of RNA polymerase I show that, subunits A14 and A43 form the heterodimer A14/43, which is distantly related to Rpb4/7 in Pol II and C17/25 in Pol III [1]. Crystal structure analysis show that A43-A14 heterodimer forms the stalk that provides a platform for initiation factors and interacts with newly synthesized RNA [3].

1: Functional architecture of RNA polymerase I. Kuhn CD, Geiger SR, Baumli S, Gartmann M, Gerber J, Jennebach S, Mielke T, Tschochner H, Beckmann R, Cramer P; Cell. 2007;131:1260-1272. PMID:18160037

2: RNA polymerase I structure and transcription regulation. Engel C, Sainsbury S, Cheung AC, Kostrewa D, Cramer P; Nature. 2013;502:650-655. PMID:24153182

3: Crystal structure of the 14-subunit RNA polymerase I. Fernandez-Tornero C, Moreno-Morcillo M, Rashid UJ, Taylor NM, Ruiz FM, Gruene T, Legrand P, Steuerwald U, Muller CW; Nature. 2013;502:644-649. PMID:24153184