![ns2 np1 ns2 np1](https://media.cheggcdn.com/media/2cd/2cd2d2ff-0437-4fb7-8321-a9dc5f7cda13/php8hcjS0.png)
NS1-70 contains the origin DNA-binding/endonuclease and helicase domains of NS1, but not the C-terminus, and the function of NS1-70 is unknown. However, NS2 is essential for HBoV1 DNA replication in primary human airway epithelium cultured at an air-liquid interface (HAE-ALI) cells 11. Non-structural proteins NS2, NS3, and NS4 are dispensable for viral replication in HEK293 cells, although these proteins contain functional domains of NS1 11. The C-terminal is a transactivation domain 22, 23, 24, 25. The ATPase and helicase domains are located in the middle of NS1 17, 23. The N-terminal domain of NS1 harbors the recognition site of the viral replication origin and the endonuclease active site 22.
![ns2 np1 ns2 np1](https://i.ytimg.com/vi/1eQsCzJn_Yw/maxresdefault.jpg)
The HBoV1 NS1 protein is a multifunctional protein that is essential for viral replication 9. A unique feature of HBoV1 is the expression of the non-structural protein of NP1, which has been reported to be required for efficient viral DNA replication 9, 19, reading through of the proximal polyadenylation site 9, 20, regulating RNA splicing 12, 21 and the production of VP mRNAs 9, 12, 21.
![ns2 np1 ns2 np1](https://image.slidesharecdn.com/periodictable-131009101040-phpapp02/95/periodic-table-21-638.jpg)
The non-structural protein rep or NS1 and the hairpin structures are essential in both replication models. The replication of parvovirus adeno-associated virus type 2 is proposed as a rolling-hairpin replication model 16, 17, while parvovirus B19V adopts a hairpin-independent replication model 18. The open reading frame in the middle of the viral genome encodes a non-structural protein NP1 9, 10, 11, 15. The N-terminus of the VP1 unique region includes a phospholipase A2 (PLA2) domain, which is involved in the parvovirus infectivity 13, 14. The right half of the genome encodes structural proteins VP1, VP2 and VP3 9, 10, 12. The left half of the genome encodes non-structural proteins NS1, NS2, NS3, NS4 and NS1-70 9, 11. All mRNA transcripts are alternatively processed from the mRNA precursor transcribed from the P5 promoter on the left of the genomic DNA 8, 9, 10. HBoV1 contains a single-stranded DNA genome of 5.5 kb with hairpins at both ends, which are essential for viral DNA replication. In most cases, HBoV1 was found to be co-infected with other viruses 7. The prevalence of HBoV1 infection is 1.5–11.3%, and most detections occur in young children with upper or lower respiratory tract diseases 3, 4, 5, 6. In addition to human parvovirus B19 (B19V), HBoV1 is the second member of the Parvoviridae family to be potentially associated with human diseases. HBoV, bovine parvovirus (BPV) and minute virus of canines (MVC) belong to the Bocaparvovirus genus in the Parvoviridae family 1, 2. Human bocavirus 1 (HBoV1) was first identified in pooled human respiratory tract samples in 2005 1.