The genome of human parvovirus B19 encodes four other proteins in addition to VP1 and VP2. The most notable of which is the large nonstructural protein commonly referred to as NS1. NS1 sequence-specifically binds and cleaves DNA via restriction endonuclease activity at its N-terminus. NS1 is responsible for the regulation of certain cellular promoters including the p21/WAF1 promoter, and is thought to regulate the virus' own promoter. The 11 kDa protein encoded by the viral genome has been implicated in viral DNA replication.
