Multifunctional protein which displays endonuclease and helicase activities required for initiating and directing viral DNA replication. Also plays a role in viral packaging and transactivation of several promoters. Binds site-specifically to 2-3 approximate tandem copies of the tetranucleotide 5'TGGT3' within the origins of replication (Ori), unwinds this hairpin region and nicks one DNA strand thereby initiating the rolling circle replication (RCR). Cooperatively binds Ori with host PIF and probably other host factors, which activate the nickase function of NS1. Becomes covalently attached to the 5' end of the nick and provides a 3'OH for priming DNA synthesis. The helicase activity unwinds DNA in a 3'-5' direction on the longer strand. Participates in the transcriptional regulation of several promoters including the viral p38 promoter that regulates the expression of VP1 and VP2 transcripts. Inhibits the host cell cycle during the G1/S transition, the S-phase, and the G2/M transition. These arrests may provide essential cellular factors for viral DNA replication. Promotes apoptosis in host cell. ATP + H2O = ADP + H(+) + phosphate The endonuclease active site can probably bind other divalent cations. Homooligomer; when bound to DNA (By similarity). Interacts with human SYNCRIP. Interacts with host transcription factor SP1; this interaction allows high levels of viral P38 promoter transactivation by NS1 (By similarity). In the N-terminus, the endonuclease region is involved in binding to the origin of replication. In the middle, there are the ATPase and helicase activities (By similarity). The C-terminus probably contains a transactivation domain (By similarity). Phosphorylated. Belongs to the parvoviruses initiator protein NS1 family.