Multifunctional protein essential for viral DNA replication, which cooperatively interacts with the viral DNA origin of replication and transactivates several promoters including the viral p6 promoter (PubMed:27809499, PubMed:24418564, PubMed:11853402). Binds the origin of replication and performs an endonucleolytic nick within a conserved sequence in the viral genome, thereby initiating the rolling circle replication (RCR) (PubMed:27809499). Participates in the transcriptional regulation the viral p6 promoter that regulates all viral transcripts and the cellular CDN1A or IL6 promoters (PubMed:8970971, PubMed:11853402). Transactivates several host promoters some of which induce the S cell cycle phase for the production of host replicative proteins (PubMed:20890043, PubMed:15518826, PubMed:24049177). Up-regulates the expression of host E2F4 and E2F5 and interacts with both these factors thereby inhibiting the host cell cycle G2/M transition (PubMed:20890043). This arrest promotes apoptosis for viral release (PubMed:20890043, PubMed:9525624). ATP + H2O = ADP + H(+) + phosphate The endonuclease active site can probably bind other divalent cations. Optimum pH is 7.0-7.5. Homooligomer; when bound to DNA (PubMed:27809499). Interacts with host E2F4 and E2F5; these interactions promote the nuclear import of E2F4 and E2F5 and the G2/M block observed in host cells (PubMed:20890043). Interacts with host transcription factor SP1; this interaction is important for NS1 transcriptional regulation of p21/WAF1 (PubMed:15518826, PubMed:11853402). Interacts with host transcription factor SP3 (PubMed:11853402). In the N-terminus, the endonuclease region is involved in binding to the origin of replication on the viral DNA as well as to the overlapping viral promoter p6. In the middle, there are the ATPase and helicase activities. The C-terminus probably contains a transactivation domain. Belongs to the parvoviruses initiator protein NS1 family.