Changes

===Virus Structure===

===Virus Structure===

van Gennip, 2005).  

van Gennip, 2005). Tautz et. al, 1999

The BVDV genome comprises a single strand of positive sense RNA which is around 12.3 kilobases in length³. The genome is read in one 3898-codon open reading frame that contains no non-coding sequences. BVDV polyprotein is translated directly from the ORF and is cleaved by viral and cellular proteinases to form mature viral proteins^{3, 4}. At either end of the ORF, 5’ and 3’ untranslated regions exist. These regions are long, allowing them to accomodate fuctions conferred in eukaryotic DNA by the 5’ cap and the 3' poly-A tail, such as controlling the initiation of translation, facilitating the entry of replicases, and contributing to RNA stability⁴.  

The BVDV genome comprises a single strand of positive sense RNA which is around 12.3 kilobases in length³. The genome is read in one 3898-codon open reading frame that contains no non-coding sequences. BVDV polyprotein is translated directly from the ORF and is cleaved by viral and cellular proteinases to form mature viral proteins^{3, 4}. At either end of the ORF, 5’ and 3’ untranslated regions exist. These regions are long, allowing them to accomodate fuctions conferred in eukaryotic DNA by the 5’ cap and the 3' poly-A tail, such as controlling the initiation of translation, facilitating the entry of replicases, and contributing to RNA stability⁴.  

BVDV's RNA genome encodes both structural and non-structural proteins. Structural proteins include ''Npro'', whose protease action generates the N-terminus of the protein ''C''. ''C'' protein packages genomic RNA and assists in the formation of the eventual enveloped virion. ''Erns'', ''E1'' and ''E2'' are all structural glycoproteins, with ''Erns'' possessing RNase activity involved in viral replication and pathogenesis⁵. 'E1'' is membrane-anchored and initiates the translocation of the antigenic ''E2'' to the envelope³.

BVDV's RNA genome encodes both structural and non-structural proteins. These include ''Npro'', whose protease action generates the N-terminus of the protein ''C''. ''C'' protein packages genomic RNA and assists in the formation of the eventual enveloped virion. ''Erns'', ''E1'' and ''E2'' are all glycoproteins, with ''Erns'' possessing RNase activity involved in viral replication and pathogenesis⁵. ''E1'' is membrane-anchored and initiates the translocation of the antigenic protein ''E2'' to the envelope³. ''P7'' has an uncertain function⁶

The next protein is P7. Although P7 function is uncertain, studies have suggested that the C-terminal part acts as a signal sequence required for correct processing and membrane translocation of NS2 (Tautz et. al, 1999).

The next protein is P7. Although P7 function is uncertain, studies have suggested that the C-terminal part acts as a signal sequence required for correct processing and membrane translocation of NS2 ().

NS2-3 is the first non-structural protein translated. Sequence similarities are shown by NS2-3 to a region that in other flaviviruses is split into two distinct polypeptides, NS2 and NS3 (Donis, 1995). NS2-3’s N-terminus is homologous to NS2, and its C-terminus to NS3. After the first 6 hours of infection, NS3 is found exclusively in cytopathic biotypes expressed as a separate polypeptide, making it a marker of cytopathic BVDV (Donis, 1995). NS2 is also expressed as a discrete polypeptide in some, but not all, cytopathic isolates.

NS2-3 is the first non-structural protein translated. Sequence similarities are shown by NS2-3 to a region that in other flaviviruses is split into two distinct polypeptides, NS2 and NS3 (Donis, 1995). NS2-3’s N-terminus is homologous to NS2, and its C-terminus to NS3. After the first 6 hours of infection, NS3 is found exclusively in cytopathic biotypes expressed as a separate polypeptide, making it a marker of cytopathic BVDV (Donis, 1995). NS2 is also expressed as a discrete polypeptide in some, but not all, cytopathic isolates.