Adenoviruses Adenoviridae

1. AdenovirusesAdenoviridae Virion Genome Genes and proteins Viruses and hosts Diseases Distinctive characteristics

2. AdenovirusesAdenoviridae • Virion • Naked icosahedral capsid (T=25) with 20 triangular faces. • Diameter 70–90 nm. • Knobbed fibers protruding from each of 12 vertices. • Eleven proteins in virion.

3. AdenovirusesAdenoviridae • Genome • Linear ds DNA, 30–36 Kb. • Short inverted terminal repeat sequence. • Both 5 ends covalently bound to a virus-coded terminal protein.

4. AdenovirusesAdenoviridae • Genes and proteins • Codes for up to 50 proteins. • Most regions of both DNA strands are transcribed by cellular RNA polymerase II. • Six early and two delayed early transcription units: E1A, E1B, E2A, E2B, E3, E4; IVa2, IX. • One major late transcription unit: five subclasses of late mRNAs, L1 through L5. • Each transcription unit gives rise to multiple mRNAs by RNA splicing. • Two small VA RNAs transcribed by RNA polymerase III.

5. AdenovirusesAdenoviridae • Viruses and hosts • Fifty human serotypes in six subgroups (A through F). • Other adenoviruses in cattle, mice, birds, etc.

6. AdenovirusesAdenoviridae • Diseases • Respiratory syndromes including pneumonia, but not common colds. • Eye and gastrointestinal infections.

7. AdenovirusesAdenoviridae • Distinctive characteristics • Multiple mRNAs arise by extensive alternative splicing. • Late transcripts made from single strong promoter and five alternative polyadenylation signals. • DNA synthesis primed by terminal protein, uses viral DNA polymerase. • Can cause tumors in experimental animals but not known to cause tumors in humans. • Adenoviruses are widely used as gene therapy and anticancer virus vectors.

8. Virion • Adenoviruses cause respiratory and enteric infections in humans • Cause of common cold, and other respiratory symptom including pneuminia • Adenoviruses can be oncogenic, but not in humans

9. Virion • Virions have icosahedral symmetry and are studded with knobbed fibers

10. Virion

11. Virion • 55 kDa virus-coded terminal protein is covalently bound to 5’ ends of viral DNA • ~ 100 bp inverted terminal repeat allows single stranded DNA to circularize, forming panhandle end • Terminal protein and inverted terminal repeats are involved in viral DNA replication

12. Virion • Fibers make contact with cellular receptor proteins to initiate infection CAR (immunoglobulin family) is cellular receptor Also use cell surface integrin protein as secondary receptor Enter by receptor mediated endocytosis, virion escape to cytosol from endosome at acidic pH Uncoating at nuclear pore

13. Genes • Expression of adenovirus genes is controlled at the level of transcription Fig. 12.4 Transcriptional map and gene products of adenovirus type 5.

14. Genes and proteins • E1A proteins are the kingpins of the adenovirus growth cycle Fig. 12.5 Major E1A proteins and interactions with cellular proteins.

15. Genes and proteins • E1A proteins bind to the retinoblastoma protein and activate E2F, a cellular transcription factor • E1A proteins also activate other cellular transcription factors • E1A binds to histone acetyl transferase • Histone acetylation results in relaxed chromation structure, more accessible to transcription factors

16. Genes and proteins Fig. 12.6 S-phase gene activation by E1A protein.

17. Genes and proteins • E1A proteins indirectly induce apoptosis by activation of cellular p53 protein Fig. 12.7 Degradation pathway of p53 is blocked by E1A protein.

18. Genes and proteins • E1B proteins suppress E1A-induced apoptosis, allowing viral replication to proceed

19. Genes and proteins • The preterminal protein primes DNA synthesis carried out by viral DNA polymerase • Single-stranded DNA is circularized via the inverted terminal repeat Fig. 12.8 Adenovirus DNA replication.

20. Genes and proteins • The major late promoter is activated after DNA replication begins • Five different poly(A) sites and alternative splicing generate multiple late mRNAs

21. Genes and proteins Fig. 12.9 Five different poly(A) sites and alternative splicing generate multiple late mRNAs

22. Genes and proteins • The tripartite leader ensures efficient transport of late mRNAs to the cytoplasm • E1B 55K and E4 orf6 complex • Nuclear export signal • selective transport of late mRNAs • The tripartite leader directs efficient translation of late adenovirus proteins • eIF4F phosphorylated by adenovirus • Host protein synthesis blocked • Viral mRNA translation continues • Because leader allows ribosome shunting

23. Genes and proteins • Adenoviruses kill cells by apoptosis, aiding virus release • E3 11.6 Kda death protein • expressed at high level during latre phase • membrane glycoprotein (ER, Golgi, nuclear membrane) • mechanism unknown • E4 orf • Induce cell death in p53-independent pathway • Absorption of fragmented membrane-bound vesicle into neighboring cells allows spread of progeny virus w/o exposing to host Ab

24. Genes and proteins • Cell transformation and oncogenesis by human adenoviruses • E1A stimulates uncontrolled cell cycle progression • E1A alone produces abortive transformation due to E1A-induced apoptosis • E1A and E1B 19K/55K coexpression is required for stable transformation

25. Genes and proteins

26. Adenoid Apoptosis Caspase Cyclin-dependent protein kinase Hexon Histone acetyl transferase Immunoglobulin gene superfamily Integrins Interferon Inverted terminal repeat Oncogene Penton base PKR Retinoblastoma (Rb) Ribosome shunting Secondary receptor Terminal protein Tumor suppressor protein Ubiquitin Key Terms