1 VIRUSES CHAPTER 10

2 What are Viruses? Obligate intracellular parasites Viral components –Nucleic acids –Capsid (protein) –Envelope (Lipid w/intg proteins)

3 4 overall types of viruses 1) bacteriophages - almost always DNA with a protein capsid. Lytic and lysogenic types 2) DNA viruses of Eukaryotes - often have phospholipid envelope outside of capsid 3) RNA viruses - have RNA as genetic material. Often hypermutable 4) RNA retroviruses - have reverse transcriptase. Many can integrate into host chromosome

4 Viral Shapes and Sizes Helical Icosahedral T4 and adenovirus TMV, M13

5 Some viruses T-even HIV lambda

6 Infectious Properties Viral Host range Viral specificity Viral Origins Depends on target receptor Selfish DNA? Transposable elements

7 Bacteriophage Most diverse?

8 Bacteriophages Plaque counts

9 Bacteriophages Replication

10 Bacteriophage = Virus that attacks bacteria and replicates by invading a living cell and using the cell’s molecular machinery. Structure of T2 phage DNA & protein Hershey-Chase Bacteriophage Experiment

11 Fig. 2.5: Life cycle of virulent T2 phage: Lytic cyle

12 1.T2 bacteriophage is composed of DNA and proteins: 2.Set-up two replicates: Label DNA with 32 P Label Protein with 35 S 3.Infected E. coli bacteria with two types of labeled T P is discovered within the bacteria and progeny phages, whereas 35 S is not found within the bacteria but released with phage ghosts. Fig. 2-6: Hershey-Chase Bacteriophage Experiment : Alfred Hershey

13 Composition and Structure Composition –Nucleic acid Genome size Modified bases –Protein Protection Infection Structure (T 4 ) –Size –Head or capsid –Tail Tail Tail Fibers Base Plate Head/Capsid Contractile Sheath

14 Infection of Host Cells Irreversible attachment Adsorption – LPS for T4 Nucleic acid injection Sheath Contraction lamB for

15 Bacteriophages

16 Lytic Phage Multiplication Cycle Eclipse –Early genes –Phage DNA synthesis –Late genes Intracellular accumulation Lysis and Release Total Phage Extracellular Phage Eclipse Intracellular accumulation phase Time after Infection Number of Infectious Particles Lysis

17 Assay for Lytic Phage Plaque assay –Method –Plaque forming unit (pfu) –Measures infectious particles Bacteria Phage + Phage

18 Lytic vs Lysogenic Cycle? Role of repressor Role of cro gene product Role of proteases Lytic = copies and immediately lyses Lysogenic = integrates into host chromosome “Prophage” = the latent form of phage where viral genome is incorporated into host genome

19 Bacteriophages Lysogenic Lysogeny

20 Fig Gene designation Function Transcribed by host RNA polymerase Left end Early promoters Promoter Inhibits host restriction Protein kinase T7 RNA polymerase Unknown Origin of DNA replication DNA ligase Nonessential Inactivates host RNA polymerase Endonuclease Lysozyme Helicase, primase DNA polymerase Exonuclease Promoter Virion protein Head protein Head assembly protein Major head protein Tail protein Virion protein Head protein Tail protein DNA maturation Transcribed by T7 RNA polymerase Proteins for DNA replication and host lysis Phage structural components and maturation proteins Bacteriophage T7 1. Replication cycle requires 25 minutes 2. Genome is linear double-stranded DNA of 39,737 bp 3. T7 encodes all of its own proteins for DNA replication and transcription 4. Time to complete 100 T7 genome copies from a single copy: 5 minutes 5. Burst size (Escherichia coli host): about 300 virions/cell 6. Head size, 45 nm 7. Forms large plaques 8. T7 promoters are unique and widely used in biotechnology 8

21 Events Leading to Lysogeny Circularization of the phage chromosome –Cohesive ends Lygase Closed Circle Cohesive Ends Linear Double Stranded Opened Circle

22 Events Leading to Lysogeny Site-specific recombination –Phage coded enzyme Repression of the phage genome – Repressor protein – Specific – Immunity to superinfection gal bio gal bio gal bio

23 Termination of Lysogeny Induction –Adverse conditions Role of proteases –recA protein –Destruction of repressor Excision Lytic growth gal bio gal bio gal bio gal bio Gene expression

24 Significance of Lysogeny Model for animal virus transformation Lysogenic or phage conversion –Definition: A change in the phenotype of a bacterial cell as a consequence of lysogeny Modification of Salmonella O antigen Toxin production by Corynebacterium diphtheriae

25 Types of Bacteriophage Lysogenic or temperate phage: Phage that can either multiply via the lytic cycle or enter a quiescent state in the bacterial cell. (e.g.,  ) –Expression of most phage genes repressed –Prophage –Lysogen

26 Viruses part II - Animals and Plants Unique challenges. Must evade immune systems and must cross 2 lipid bilayer barriers. (ie cross into nucleus)

27 RNA Viruses Chromosomal Arrangements – + strand (directly transcribed) – – strand – Double strand

28 RNA Virus Families 11 RNA virus families –Picornaviridae (fmdv, polio) –Togaviridae (rubella) –Flaviviridae (hep C, west nile, yellow fever) –Orthomyxoviridae (flu) RNA viruses more prone to mutation

29 Fig

30 RNA Virus Families (cont.) Retroviridae (hep B, htlv)-retrovirus reverse transcriptase Paramyxoviridae (measles, mumps, pneumonia) - ss strand

31 RNA Virus Families (cont.) Rhabdoviridae (rabies)

32 RNA Virus Families (cont.) Orthomyxoviridae (all influenza)

33 RNA Virus Families (cont.) Filoviridae Bunyaviridae Arenaviridae Reoviridae

34 DNA Virus Families Adenoviridae Herpesviridae Poxviridae

35 DNA Virus Families (cont.) Papovaviridae Hepadnaviridae

36 DNA Virus Families (cont.) Parvoviridae Emerging viruses

37 Viral Replication Activities –Adsorption –Penetration (virus or chromosome) –Synthesis –Maturation –Release

38 Animal Viruses DNA viruses Envelope derives from cells own plasma membrane

39 Animal Viruses RNA viruses Latent viruses retroviruses

40 Culturing Animal Viruses Live animals Eggs

41 Culturing Animal Viruses Cell Culture –Primary –Continuous

42 Viral Cytopathic Effects Cytopathy Teratogenic effects Japanese word for “little monsters” mutations that affect tissue growth Damage to cells

43 Viruslike Agents PLANTS Satellites Viroids

44 Viruslike Agents Prions Kuru Creutzfeld-Jacob BSE Scrapie Alpha helixB-pleated sheet

45 Viruses and Cancer Mechanism of cancer causation HPV

46 Viruses and Cancer Oncogenes/proto-oncogenes V-myc V-ras Rous Sarcoma Virus RSV Kaposi’s sarcoma - appears when immune system depressed probably by herpes virus 8

47 Viruses to know something about HPV (DNA) HIV (RNA) Flu (RNA) Adenovirus(DNA) Herpes(DNA)

48 Herpes Simplex After initial infection, the viruses move to sensory nerves, where they reside as life-long, latent viruses.

49 HPV human papilloma virus Causes warts and some strains cause cervical cancer teratogenic

50 HIV human immunodeficiency virus RNA retrovirus T-cell host (CD4 + T-killer cells) needs protease to replicate binds to CCR5 and CD4 receptors

51 Adenovirus Common cold Usually affects respiratory tract. sometimes engineered for gene therapy DS DNA virus

52 Influenza H = hemaglutinin N = neuraminidase RNA virus mutates rapidly animal reservoirs can cross species lines