This domain family is found in Bacillus. Members of this family are Swra proteins involved in swarming motility (a multicellular movement of hyper-flagellated cells on a surface). SwrA is a key transcription factor facilitating this cascade. It acts synergistically with DegU to drive the fla/che operon encoding flagella components, chemotaxis constituents and the alternative sigma factor sigmaD, which is regarded as the primary event in the development of motility [1]. LonA protease of Bacillus subtilis inhibits SwrA by proteolytically restricting its accumulation [2]. SwrA does not contain any known DNA binding domain, and it has been shown to interact with the N-terminal domain of DegU. Anecdotally, in most laboratory strains, e.g. 168, the swrA coding sequence contains a nucleotide insertion that prematurely interrupts its reading frame, causing a non-swarming phenotype strain [3].

1: SwrA regulates assembly of Bacillus subtilis DegU via its interaction with N-terminal domain of DegU. Ogura M, Tsukahara K; J Biochem. 2012;151:643-655. PMID:22496484

2: Adaptor-mediated Lon proteolysis restricts Bacillus subtilis hyperflagellation. Mukherjee S, Bree AC, Liu J, Patrick JE, Chien P, Kearns DB; Proc Natl Acad Sci U S A. 2015;112:250-255. PMID:25538299

3: The role of SwrA, DegU and P(D3) in fla/che expression in B. subtilis. Mordini S, Osera C, Marini S, Scavone F, Bellazzi R, Galizzi A, Calvio C; PLoS One. 2013;8:e85065. PMID:24386445