Question

Describe the biosynthesis of human papillomavirus (HPV). Discuss the transcription of the virus genome into new virion particles. Make sure to include if your virus must package any special enzymes in order to be effective.

Answer 1

Human papillomavirus (HPV) biosynthesis has been studied only in the live cells during lysogenic replication cycle due to its inability to propagate in the tissue cultures.

It enters into the skin from the surface crevices after binding and then incorporates its genome into the nucleus. where the sequential transcription of the genes happens. This leads to the synthesis of more viral proteins and then the capsid. Assembly and packaging of the whole virus takes place in the cytosol and multiple copies are generated.

Virion particle (Viral-like particles) generation is dependent on the differentiation of the keratinocytes in the epithelium where virus infects. It is also induced by the addition of certain differentiation factors like '12-O-tetradecanoyl phorbol-13-acetate' in the organotypic cultures.

HPV is a double-stranded circular DNA virus where transcription of the genome occurs from only one DNA strand, yielding multiple mRNAs with several open reading frames. After the transcription of early (E genes) and late (L genes) synthesis genes, viral genome and capsid are generated and released extracellularly as virion particles. Hence, these are the complete, infective form of a virus present outside the host.

Special enzyme - expressed by HPV is E1 which is an ATP-dependent helicase required for the initiation of viral DNA replication.