VIRUS PROPERTIES

1. VIRUS PROPERTIES • Infectious – must be transmissible horizontally • Intracellular – require living cells • RNA or DNA genome, not both* • Most all have protein coat* • May of may not have lipid envelope • May have broad or narrow host range • Replication involves eclipse (breaking apart of virus particles) and reassembly • Use host factors for to complete replication cycle

2. SOME CONSEQUENCES AND EFFECTS OF VIRUS INFECTION • Like other life forms, viruses promote the propagation of their own kind • Like other life forms, virusesevolve in response to selection pressure • Viruses are major factors in promoting the evolution of higher organisms • Viruses help control populations of their hosts, including humans

3. Virus-like agents classified and studied with viruses • Viroids • No coat protein, no coding capacity • Prions • No nucleic acid (?) • Retrotransposons • No infectivity (?)

4. Host properties influence the virus types found in that host group • Vertebrates have broad range of viruses • Plants have mostly small RNA viruses • Fungi have mostly dsRNA viruses • Single-celled organisms have mostly large dsDNA viruses

5. Viruses are submicroscopic intracellular pathogens

6. Sizes of microscopic and submicroscopic biological entities and their ability to be examined using various technologies Flint et al., 2004 Principles of Virology Fig. 1.8

7. Viruses may be simple or complex • Genome sizes 0.3 - 1200 kb; average genome sizes vary with host organism types • Isometric particle sizes vary from ~24 nm to ~400 nm diameter • May have single-stranded (ss) or double-stranded (ds) RNA or DNA genome • If ssRNA, may be + or – sense • May have one or many proteins in particles • May or may not have lipid envelope

8. Types of viral genomes • double-stranded (ds) DNA • Rarely segmented • Often large • single-stranded (ss) DNA • Rarely large • Less common than dsDNA • ssRNA, negative sense • Often found in viruses with broad host ranges • ssRNA, positive sense • Most common overall • dsRNA • Often segmented • Particle structure often critical

9. Composition of viruses infecting different hosts • No “rules” about virus families that may or may not be present in a given kingdom • Some types of viruses are found more commonly in some kingdoms than in others • Many plant viruses contain ssRNA genomes • Many fungal viruses contain dsRNA genomes • Many bacterial viruses contain dsDNA genomes • Host properties determine the types of viruses that tend to be found in members of a biological “kingdom”

10. Virus types by nucleic acid composition DNA RNA ss ds ss ds env naked env naked env naked env naked Families Species 0 5 9 12 9 14 2 5 0 100 200 300 200 600 10 300 Host type Vertebrate Invertebrate Plant Fungus Bacteria - + ++ ++ ++ ++ - ++ - + ++ - ++ ++ - ++ - ++ - + + +++ - + - - - + + + + +++ - + + +++ - + + -

11. Animal RNA – 5-30 kb DNA: 5-350 kb Many enveloped Range of complexity Range of morphologies Some divided genomes • True Fungi • RNA – 2.5-28 kb • DNA – none • Enveloped ones have no capsid • Little genome complexity • Little morphological complexity • Some divided genomes • Plant • RNA – 0.3-28 kb • DNA – 3-10 kb • Few enveloped • Little genome complexity • Little morphological complexity • Many divided genomes Overview of Virus Properties • Prokaryote • RNA – 5-8 kb • DNA – 10-200 kb • Few enveloped • Range of complexity • Range of morphologies • Few divided genomes • Lower eukaryote • RNA – 5-10 kb • DNA – 180-1200 kb • Internal envelope • Range of complexity • Range of morphologies • No divided genomes

12. Tobacco mosaic virus – a typical small RNA virus • 18X300 nm • Single 6400 nt RNA • 2130 copies of single 17 kDa coat protein • 3 essential genes • Simple regulatory elements

13. Poxvirus – a typical large dsDNA virus • 120X200 nm • Single 180 kb DNA • Complex coat made up of numerous proteins • >100 essential genes • Complex regulatory elements

14. Virus at the edge: Mimivirus • Mimivirus infects Acantamoeba polyphaga • 400 nm particle, 1.2 megabase genome, 1262 putative ORFs represent the largest virus identified yet • Many genes for normal cellular functions • central translation functions • Aminoacyl tRNA synthetases • Peptide release factor 1 • Translation elongation factor EF-TU • DNA repair enzymes • Many polysaccharide synthesis enzymes • Lineage suggests connection with eukaryotes, not prokaryotes Raoult et al., Science Express 10/14/04

15. Phylogenetic position of Mimivirus Compared to other similar DNA viruses Compared to other prokaryotic and eukaryotic life forms Raoult et al., Science Express 10/14/04

16. Mimiviruses (arrowed) can bee seen inside their amoeba host, Acanthamoeba polyphaga using a light microscope Raoult et al., Science Express 10/14/04

17. By transmission electron microscopy, isolated Mimivirus can be seen as a large icosahedral virus with fibrilar protrusions Mimivirus (green) seen by fluorescence microscopy in amoeba Mimivirus in ultrathin section in amoeba Raoult et al., Science Express 10/14/04

18. At 1.2 megabases (1.2X106 nucleotides), Mimivirus has the largest genome of any known virus, larger than many bacteria

19. Simple virus replication cycle • Virus enters • host cell 5. New virus released from host cell 2. RNA released; translates 3. Replication in cytoplasm 4. New virus assembled

20. From 7th Report of the ICTV (Academic Press, 2000)

21. From 7th Report of the ICTV (Academic Press, 2000)

22. From 7th Report of the ICTV (Academic Press, 2000)

23. From 7th Report of the ICTV (Academic Press, 2000)

24. From 7th Report of the ICTV (Academic Press, 2000)

25. From 7th Report of the ICTV (Academic Press, 2000)

26. From 7th Report of the ICTV (Academic Press, 2000)

27. From 7th Report of the ICTV (Academic Press, 2000)

28. From 7th Report of the ICTV (Academic Press, 2000)

29. From 7th Report of the ICTV (Academic Press, 2000)