Viruses with Animal Host

Differences with Viruses and Animal Hosts

• require different mechanisms of penetration, biosynthesis and release

• host specific

• tissue specific (tissue tropism)

Life cycle of viruses with animal hosts

1. virus attaches to target epithelial cell

2. cell engulfs virus via endocytosis

3. fusion and uncoating of viral RNA

4. viral RNA enters nucleus were it is replicated by viral RNA polymerase

5. viral mRNA is used to make viral proteins

6. viral particles are released into extracellular fluid

7. cell continues to make more of virus

RNA viruses with +ssRNA

• positive single strand RNA

• can be directly read by the ribosomes to synthesize viral proteins

RNA viruses with -ssRNA

• must first use -ssRNA as a template for synthesis of +ssRNA before viral proteins can be synthesized

Viral RNA Dependent Polymerase

• replicate -ssRNA into +ssRNA so that the ribosomes can translate it

RdRP (viral RNA-dependent RNA polymerase)

• brought in by the virus

• used to make +ssRNA from -ssRNA

• important for replication of dsRNA viruses

What does RdRP do for dsRNA viruses

• uses negative strand as a template to create +ssRNA

How do +ssRNA become viral proteins

• host ribosomes translate it

Reverse Transcriptase

• convert ssRNA into dsDNA

Retroviruses

• have positive strand RNA genome

• genomes do NOT function as mRNA

Steps in Retroviruses

• ssRNA is converted into dsDNA using reverse transcriptase

• dsDNA integrates into host DNA where it serves as template for mRNA synthesis and synthesis of plus-strand RNA genome

What does DNA-depednet RA polymerase do

• catalyze synthesis of plus strand RNA

• mRNA synthesis from when dsDNA integrates into host DNA

dsDNA

• in retroviruses, it integrates into host cell genome and becomes permanent part of host

• serves as template for mRNA synthesis and genome synthesis

Provirus

• integrated viral genome in retroviruses

HIV

• causes acquired immunodeficiency syndrome

• member of Lentivirus

HIV-1

• retrovirus

• enveloped virus

• two copies of RNA genome

• uses reverse transcriptase and integrase

Steps in HIV

1. HIV fuses with host cell surface

2. HIV RNA, transcriptase,integrase, and viral proteins enter host cell

3. Viral DNA is formed by reverse transcription

4. Viral DNA is transported across nucleus and integrates into host DNA

5. New viral RNA is used as genomic RNA and to make viral proteins

6. new viral RNA and proteins move to cell surface and new HIV forms

7. virus matures when proteases release proteins that form mature HIV

HIV binding

gp120 binds to CT4+ T cells, macrophages, dendritic cells and monocytes

• virus enters by receptor mediated endocytosis

• needs coreceptors to enter cell

Reverse Transcriptase

• RNA dependent DNA polymerase

• DNA dependent DNA polymerase

• error prone, has no proofreading capability

Acute Infection

• symptoms worsen over short period followed by elimination of virus and recovery

Persistent Infection

• virus stays in certain tissues or organs of infected person

Latent Infection

• virus stays hidden or dormant inside cell

Chronic

• disease with symptoms tat can be recurrent over long time