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Table 2 Representation of the five classes of viral genes in three selected viruses with small, medium-size and large genomes

From: The ancient Virus World and evolution of cells

  Genome size (kb)/number of annotated genes Representation of the 5 classes of viral genes (number and brief description)
   1. Recent acquisitions from cells 2. Ancient acquisitions from cells 3. ORFans 4. Conserved virus-specific genes 5. Hallmark genes
Virus       
Poliovirus a 7.4/10 None 2: a duplication of a chymotrypsin-like protease (3C, 2A) 1: uncharacterized protein (3A) 1: genome-linked protein (VPg) 6: 4 diverged copies of JRC (VP1-4), S3H (3C), RdRp (3D)
Sulfolobus turreted icosahedral virus (STIV) b 17.6/36 3: two predicted transcription regulators and an uncharacterized protein 5: four predicted transcription regulators and an uncharacterized protein 26: uncharacterized proteins None 2: JRC, packaging ATPase
Vaccinia virus c 194.7/~200 ~48: primarily, proteins involved in virus-host interaction ~36: primarily, proteins involved in genome replication and expression ~24: poorly characterized proteins, possibly, involved in virus-host interactions ~84: primarily, structural components of the virion and some proteins involved in genome expression 5: JRC, S3H/primase, packaging ATPase, DNA polymerase(?)
  1. aThe classification is based on the analysis described in [87].
  2. bThe classification is based on the analysis described in [11].
  3. cThe classification is based on the analysis described in [108] and EVK, unpublished observations; the uncertainty in the number of genes is due to the pseudogenization of varying subsets of genes in different strains of vaccinia virus.