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LECTURE 12:. Virus Genome Replication. Waqas Nasir Chaudhry. Viro100: Virology 3 Credit hours NUST Centre of Virology & Immunology. Transcription of virus genomes. There are four main categories of virus genome: dsDNA , ssDNA , dsRNA and ssRNA

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virus genome replication


Virus Genome Replication




3 Credit hours

NUST Centre of Virology & Immunology

transcription of virus genomes
Transcription of virus genomes
  • There are four main categories of virus genome: dsDNA, ssDNA, dsRNA and ssRNA
  • Because of distinct modes of transcription within the dsDNA and ssRNA categories a total of seven classes of viruses can be recognized
  • This division of the viruses into classes based on genome type and mode of transcription was first suggested by David Baltimore
or genome
(+) or (−) Genome
  • This labelling is relative to the virus mRNA, which is always designated (+).
  • A nucleic acid strand that has the same sequence as mRNA is labelled (+) and a nucleic acid strand that has the sequence complementary to the mRNA is labelled (−)

Some DNA viruses have ability to

carry out reverse transcription;

these viruses known as pararetroviruses and

Class VII was formed to accommodate them i.e. Badnavirus of plants

ambisense genome
Ambisense Genome

There are a few single stranded nucleic acids of viruses where there is a mixture of (+)and(−) polarity within the strand, in other words there are open reading frames (ORFs) in both directions.

Example Sendai Viruses

modi cations to the central dogma
Modifications to the central dogma
  • In 1958 Francis Crick proposed a ‘central dogma of molecular biology’
  • Which stated that the flow of genetic information is always from DNA to RNA and then to protein, with genetic information transmitted from one generation to the next through copying from DNA to DNA

Increasing understanding of how viruses replicate their genomes necessitated some modifications to this dogma in 1970; many viruses have RNA genomes that are copied to RNA, and some viruses copy from RNA to DNA

Modifications to the central dogma