This is one of two Tudor-like domains found in the N-terminal region of RapA proteins. RapA is an abundant RNAP-associated protein of 110-kDa molecular weight with ATPase activity. It forms a stable complex with the RNAP core enzyme, but not with the holoenzyme. The ATPase activity of RapA increases upon its binding to RNAP [1]. The N-terminal region of RapA contains two copies of a Tudor-like domains, both folded as a highly bent antiparallel beta-sheet. This fold is also found in transcription factor NusG , ribosomal protein L24, human SMN (survival of motor neuron) protein, mammalian DNA repair factor 53BP1, putative fission yeast DNA repair factor Crb2 and bacterial transcription-repair coupling factor known as Mfd. The functional roles of the N-terminal region homologs in these proteins suggest that the Tudor-like domains of RapA may interact with both nucleic acids and RNAP [2].

1: Structural basis for transcription reactivation by RapA. Liu B, Zuo Y, Steitz TA; Proc Natl Acad Sci U S A. 2015;112:2006-2010. PMID:25646438

2: Structure of RapA, a Swi2/Snf2 protein that recycles RNA polymerase during transcription. Shaw G, Gan J, Zhou YN, Zhi H, Subburaman P, Zhang R, Joachimiak A, Jin DJ, Ji X; Structure. 2008;16:1417-1427. PMID:18786404