Multifunctional protein which displays endonuclease and helicase activities required for initiating and directing viral DNA replication (PubMed:12050365). Also plays a role in viral packaging and transactivation of several promoters (PubMed:7636987). 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) (PubMed:17898054, PubMed:12050365, PubMed:9349487). Cooperatively binds Ori with host PIF and probably other host factors, which activate the nickase function of NS1 (PubMed:11435581, PubMed:12050365). Becomes covalently attached to the 5' end of the nick and provides a 3'OH for priming DNA synthesis (PubMed:12050365). The helicase activity unwinds DNA in a 3'-5' direction on the longer strand (PubMed:12050365). Participates in the transcriptional regulation of several promoters including the viral p38 promoter that regulates the expression of VP1 and VP2 transcripts (PubMed:7636987, PubMed:8551622). Inhibits the host cell cycle during the G1/S transition, the S-phase, and the G2/M transition (PubMed:9188601, PubMed:11602746). These arrests may provide essential cellular factors for viral DNA replication. Promotes apoptosis in host cell (PubMed:21295324). 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 (PubMed:9847309). Interacts with host transcription factor SP1; this interaction allows high levels of viral P38 promoter transactivation by NS1 (PubMed:7799962, PubMed:9454706). In the N-terminus, the endonuclease region is involved in binding to the origin of replication (By similarity). In the middle, there are the ATPase and helicase activities (By similarity). The C-terminus probably contains a transactivation domain (PubMed:7799962). Phosphorylated. Belongs to the parvoviruses initiator protein NS1 family.