Replication of Medium DNA Virus; ssDNA Virus

Family Adenoviridae “gland” lymphoid tissue in nasopharynx Icosahedral capsid, nm Fiber projections (ligand for attachment) Some adenovirus produce tumors in experimental animals (hamsters)

Genus: Mastadenovirus “breast” Mammalian species Human adenovirus 1-50 Monkeys, horses, cows, pigs, dogs

Genus: Aviadenovirus “bird” Avian species

Adenovirus Isolated in 1953 when searching for common cold virus in tonsil & adenoid tissue culture Latent virus activated, replicates, CPE (cytopathic effect) of cells

Adenovirus Infections Upper & lower respiratory infection (URTI, LRTI) Epidemic conjunctivitis Gastroenteritis Acute hemorrhagic cystitis Lytic, chronic, latent, transform cells

URTI: “Cold” Rhinovirus Coronavirus Adenovirus Parainfluenza virus

URTI: Pharyngitis Adenovirus Herpes simplex virus (HSV) Enterovirus Epstein-Barr virus (EBV) Less likely: Influenza virus, Parainfluenza virus, Rhinovirus, Coronavirus

URTI/LRTI: Croup (Laryngotracheobronchitis) Parainfluenza virus Respiratory syncytial virus

LRTI: Bronchiolitis Parainfluenza virus Respiratory syncytial virus (RSV)

LRTI: Pneumonia (Lung) Influenza virus Respiratory syncytial virus (RSV) Parainfluenza virus Adenovirus virus Coronavirus

“Cold” Virus Symptoms Fever Cough Headache Sore throat Muscle ache Fatigue ± Vomiting, diarrhea

Feels Like a “Cold” But It’s Not! See Clinician if: Fever >103°F Fever 101°F for more than 3 days Yellow/green discharge from lungs Extreme difficulty swallowing Shortness of breath Chest pains Earache, discharge from ears, hearing loss

Adenovirus Genome: dsDNA Linear, 36 kbp Ends have inverted terminal repeats (ssDNA forms circular structure) 5’ end - viral terminal protein (TP, 50 Kd) Genes found on both DNA strands Express proteins for: cell activation, DNA synthesis, suppress host immune & inflammatory response, structural capsid

Adenovirus“Early” mRNA From both DNA strands using cell RNA pol II –“right” strand transcription (--->) –“left” strand transcription (<---) Four early transcription “units”: E1 – E4 –each with separate promoter –E1 enhanced promoter activated by host cell DNA binding proteins mRNAs: 5’cap, 3’polyA tail, post-transcriptionally spliced

Adenovirus: “Early” Proteins E1 – transformation function, binds cell repressor proteins p105RB & p53 E2 – DNA pol, TP, DNA-binding protein (shuts off early promoter) E3 – decreases host MHC proteins & inflammation E4 – decrease host T cell recognition

Host Cell Activation Adenovirus E1 protein binds cell p105 RB protein p105 RB no longer functions to down regulate cell transcription Cell remains active

Adenovirus DNA Replication “Continuous” DNA strand synthesis Replication complex: –viral DNA pol –TP (primer) –DNA-binding proteins (viral & cellular) Type 1 Replication: –#1 strand copied into dsDNA –#2 strand displaced into ssDNA intermediate Type 2 Replication: displaced ssDNA copied into dsDNA

Adenovirus: “Late” mRNA From one DNA strand – “right” strand transcription (--->) Single promoter: leader + five mRNAs (L1 – L5) by alternative splicing Translate mainly for structural proteins

Adenovirus: Splicing of mRNA First observation for splicing of eukaryotic mRNA Hybridize late “hexon” mRNA with single strand viral DNA EM observation that ds RNA:DNA not co-linear, with ssDNA “loops” Deduce that mRNA must be shorter (“exons” – 1,2,3 leader, hexon) and lack certain DNA regions (“introns”- A,B,C)

Adenovirus: Virus- Associated (VA) RNA By cell RNA pol III Short RNA molecule blocks antiviral action of interferon (stops activation of PKR) Also, E1A protein blocks interferon signal transduction Role in persistent viral infection

Adenoviral Vector for Gene Replacement Therapy Eliminate & cut out viral pathogenic gene Insert therapeutic gene, i.e. insulin gene Infect patient with virus vector to produce insulin in pancreas Complications due to adenovirus infection of various other organs, results in toxicity Vector DNA eventually degraded by cell

Family Parvoviridae “small” ssDNA, 5.5 kb icosahedral capsid, nm Genus: Parvovirus – mammals and birds Genus: Dependovirus (adeno-associated viruses) requires “helper” adenovirus for replication Genus: Densovirus - insects

Human Parvovirus B19 Infects mitotically active erythroid precursor cells in bone marrow Erythemia infectiosum (fifth disease) in children – mild flu-like, “slapped cheek” rash Aplastic crisis in hemolytic anemia and in sickle-cell patients Associated with rheumatoid arthritis

Reading & Questions Chapter 16: Replication Strategies of Small and Medium-Sized DNA Viruses

Class Discussion – Lecture Is there any similarity in function of adenovirus and SV40 virus “early” proteins? 2. Although adenovirus has a dsDNA genome, why can’t you assign polarity (+/-) to the two strands? 3. As human parvovirus, unlike SV40, does not have the ability to activate its host cell, how does it insure it will infect a cell that is actively dividing?