MERS-CoV ORF8b, BECV protein I, and related Embecovirus and Merbecovirus proteins
This family includes the ORF8b accessory protein from Middle East respiratory syndrome-related coronavirus (MERS-CoV) and related merbecoviruses (C lineage), and protein I (also known as accessory protein N2) from bovine enteritic coronavirus-F15 strain (BECV-F15) and related Embecoviruses (A lineage). The gene encoding ORF8b is an internal ORF that is overlapped by the N (nucleocapsid) protein gene (ORF8a), and the gene encoding protein I is included in the N gene as an alternative ORF. ORF8b and protein I appear to have no homologous proteins in Sarbecovirus (lineage B), which includes Severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) and SARS-CoV-2 (2019 novel coronavirus, 2019-nCoV). There are five essential genes in CoVs that result in the following gene products: Spike (S) protein, Membrane (M) glycoprotein, Nucleocapsid (N), Envelope (E) protein, and replicase/protease polyproteins (ORF1ab); all are required to produce a structurally complete viral particle. In addition, CoV genomes also contain ORFs coding for accessory proteins that are specific for certain CoV lineages or for a particular CoV. In general, CoV accessory proteins are considered dispensable for viral replication; however, several accessory proteins have been shown to exhibit functions in virus-host interactions during CoV infection. MERS-CoV ORF8b and BECV-F15 protein I are not essential for viral replication.
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