This is the small N-terminal alpha+beta domain of the DNA helicase UvsW from bacteriophage T4 [1,2], which consists of five beta-strands and two alpha-helices. This domain is structurally homologous to the DNA-binding domain of the T4 transcription factor MotA, thus, it likely binds the nucleic acid substrate [1,2].

1: The crystal structure of the UvsW helicase from bacteriophage T4. Sickmier EA, Kreuzer KN, White SW; Structure. 2004;12:583-592. PMID:15062081

2: Crystallographic and NMR analyses of UvsW and UvsW.1 from bacteriophage T4. Kerr ID, Sivakolundu S, Li Z, Buchsbaum JC, Knox LA, Kriwacki R, White SW; J Biol Chem. 2007;282:34392-34400. PMID:17878153