that affect the assembly process. Some of these viral nonstructural protein functions are replicon formation, immunomodulation, and transactivation of viral structural protein encoding genes. Replicon formation Viral nonstructural proteins interact with host cell proteins to form the replicon, otherwise known as the replication complex. In the hepatitis C virus, viral nonstructural proteins interact with cellular vesicle membrane transport protein, hVAP-33, to assemble the replicon. Viral nonstructural 4b (NS4B) protein alters the host cell's membrane and starts the formation process of the replication complex. Other viral nonstructural proteins such as NS5A, NS5B, and NS3, are also recruited to the complex, and NS4B interacts with them and binds to viral RNA. Immunomodulation The immune response of a host to an infected cell can be adjusted through the immunomodulatory properties of viral nonstructural proteins. Many species of large DNA viruses encode proteins which subvert host immune response, allowing proliferation of the virus. Such proteins hold potential in developing new bio-pharmaceutical treatments for inflammatory disease in humans, as the proteins have been proven to subvert inflammatory immune mediators. Viral nonstructural protein NS1 in the West Nile virus prevents complement activation through its binding to a complement control protein, factor H. As a result, complement recognition of infected cells is reduced, and infected cells remain unharmed by the host's immune system. Viral regulatory and accessory proteins Viral regulatory and accessory proteins have many functions. These viral proteins control and influence viral gene expressions in the viral genome, including viral structural gene transcription rates. Viral regulatory and accessory proteins also influence and adjust cellular functions of the host cell, such as the regulation of genes, and apoptosis. In DNA viruses and retroviruses, viral regulatory proteins can enhance viral gene transcription, likewise, these proteins can also enhance host cellular gene transcription too. Viral accessory proteins, also known as auxiliary proteins, are coded for by the genome of retroviruses. Most viral accessory proteins only carry out their functions in specific types of cells. Also, they do not have much influence on the replication of the virus. However, in some instances, maintaining the replication of viruses would require the help (and function) of viral accessory proteins. Endogenous retroviral proteins Syncytin is an endogenous retrovirus protein that has been captured in the mammalian genome to allow membrane fusion in placental morphogenesis. References External links List of all known Viral Proteins in UniProtKB VirusMint Virology