Systematic Veterinary Virology

REPLICATION

• The virus replicates in the cytoplasm. The virus enters into the cell through endocytosis. This is followed by partial uncoating. BTV is inactivated if complete uncoating occurs. Early transcription of the d/s RNA genome by viral polymerase occurs inside this sub-viral particle. The various genome segments are transcribed/translated at different frequencies.
• Transcription occurs in two stages, primary and secondary. Only (-) sense strands are transcribed, resulting in synthesis of (+)sense mRNAs, which are capped inside the core. These mRNAs leave the core and are translated in the cytoplasm.
• The genome is replicated in the cytoplasm in a conservative fashion. An excess of (+)sense strands are produced, which serve as late mRNAs and as template for (-)sense strand synthesis (i.e. each (-) strand leads to many (+) strands - not one-for-one as semi-conservative replication). The mechanism responsible for segregation of the various genome segments into developing particles is not known.