Here, we describe functional characterization of an early gene ( ) product of a virulent sk1 like phage, vB_Llc_bIBBF13 (abbr. F13). The GP46 protein carries a catalytically active RecA-like domain belonging to the P-loop NTPase superfamily. It also retains features characteristic for ATPases forming oligomers. In order to elucidate its detailed molecular function, we cloned and overexpressed the gene in . Purified GP46 protein binds to DNA and exhibits DNA unwinding activity on branched substrates in the presence of adenosine triphosphate (ATP). Size exclusion chromatography with multi-angle light scattering (SEC-MALS) experiments demonstrate that GP46 forms oligomers, and further pull-down assays show that GP46 interacts with host proteins involved in replication (i.e., DnaK, DnaJ, topoisomerase I, and single-strand binding protein). Taking together the localization of the gene and the obtained results, GP46 is the first protein encoded in the early-expressed gene region with helicase activity that has been identified among lytic phages up to date.