(V) 22: Viral Genomes Flashcards
Green Fluorescent Protein
Physical measurement
- a gene that will be translated into a fluorescent protein will be inserted into the viral genome
- then viral protein has a fluorescent tag
Hershey-Chase Experiment
proof that the genome is key
- what specifies the production of virus? nucleic acid or protein (shell)
viruses were grown in sulfur labeled protein capsule OR phosphorus labeled DNA core
- bacteriophage infects with radioactive precursors to DNA or protein - virus infects bacteria
- Blend - virus/phage is removed from cell and leaves genome
- Separate - cells and phages are separated by centrifugation
- get pellet (sediment/heavy) and supernatant (liquid) - Radioactive phosphorus is detected in next gen of bacteriophage
Results of Hershey-Chase Experiment
Sulfur was detected in supernatant - protein shell was radioactive
- NOT in cell
Phosphorus was detected IN the cell - pellet part
Modern-day Hershey-Chase experiment
- bacteriophage mixed w/ cyanine dye binds viral genomes
- upon infection into bacterial host, dye leaves bacteriophage and enters host interior
As phage fluorescence drops, cell’s interior fluorescence increases
- more fluorescence in nucleic acid/genome
Baltimore Classification Scheme
Nobel for work on Rev. Transcriptase
Found SEVEN groups that differ based on genome
KEY concept: viral genomes must make mRNA. The mRNA must be read by host ribosomes. mRNA is read in the 5’ to 3’ direction
Groups
+ssRNA, -ssRNA, dsRNA, dsDNA, ssRNA w/ DNA intermediate, ssDNA, gapped dsDNA (ss/dsDNA)
Changing btwn groups of Baltimore Classification Scheme
dsRNA and -ssRNA become +ssRNA via viral RNA-dependent RNA Poly
dsDNA can become +ssRNA via DNA-dependent RNA-Poly
ss/dsDNA can become dsDNA via DNA Poly or R.T. (same for ssDNA to ss/dsDNA)
+ssRNA w/ DNA intermediate can become ssDNA via viral RNA-dependent DNA Poly (R.T)
Common goal of genes
production of ss mRNA to be translated by host cell machinery
mRNA
+ strand that is ready to be translated
+DNA strand
equivalent polarity to +RNA strand
RNA or DNA complements of + strands
considered - strands
7 Types of genomes
genomes are DNA or RNA (NOT both)
RNA
ss + RNA
ss - RNA
ds RNA
ss + RNA w/ DNA intermediate
DNA
ss DNA
ds DNA
gapped ds DNA
dsDNA
DNA-dependent RNA Poly transcription makes ssRNA from dsDNA
DNA-dependent RNA Poly can be from HOST or can be encoded in VIRAL genome
Ex. Polyomaviridae, Poxviridae
Polyomaviridae
virus family within dsDNA
small genome = has to use host’s enzymes
JC Virus - most ppl infected have immune system take care of the virus
- BUT immunocompromised patients will get degenerative brain diseases due to JCV
Poxviridae
viral family in dsDNA
DNA-dependent RNA Poly is encoded IN VIRAL genome
larger genome = can make their own DNA-dependent RNA Poly
causes variola virus disease (smallpox)
Gapped dsDNA
aka ss/dsDNA (not completely complinentary)
- also contains protein and RNA
ss/dsDNA -> dsDNA -> +ssRNA
- need to make dsDNA molecule first
- Viral-associated DNA Poly “FILLS IN gaps” then host DNA-dependent RNA Poly transcription happens to make +ssRNA
Ex. Hepadnaviruses (Hep B viruses)
Hepadnaviruses
viral family in gapped dsDNA (ss/dsDNA)
causes Hep B
- now treatable but can cause liver damage
- 100x more infectious than HIV-1 = more infectious particles per normal particles
Does HIV or Hep B have a higher Particle/PFU ratio?
HIV because it is less infectious, meaning it has less infectious particles and a higher ratio
ssDNA genomes
ss DNA -> ss/dsDNA -> dsDNA -> + ssRNA
- single strands CANNOT be copied to mRNA
- host DNA Poly makes dsDNA
- host RNA Poly makes mRNA (+ssRNA)
Ex. Paroviridae
Paroviridae
viral family within ssDNA
causes paroviruses
- mostly known for cat/dog infections
- infect cells of intestine, hematopoietic system and fetus
- Ex. canine paroviruses infect and kill puppies
Viral RNA genomes
- host does NOT have an RNA-dependent RNA Poly
- so -RNA strand needs a virally encoded RNA-dependent RNA Poly to make mRNA readable by host translation machinery
dsRNA
- dsRNA CANNOT be translated
- make +RNA strand using viral RNA-dependent RNA Poly and -RNA strand as a template
- the new +RNA strand becomes mRNA
Ex. Reoviridae
Reoviridae
viral family within dsRNA
Virus: Rotavirus (not effective vaccine)
- 4/5 children in their 1st 5 yeas of live develop rotavirus
- most important cause of gastroenteritis worldwide and infant mortality in developing world
- dehydration is main contributor to mortality
- fever, diarrhea, ab pain
ss+ RNA
READY TO GO
No need for virally encoded RNA-dependent Poly
Ex. Picornaviridae, Coronoviridae
Picornaviridae
viral family within ss+RNA
causes poliovirus
- causes paralytic poliomyelitis
- disabling paralysis
- inflammation of motor neurons of spinal cord and brain stem
Coronaviridae
viral family within ss +RNA
causes SARS- CoV2
ss+RNA with DNA intermediate
“ready to go” BUT they have Reverse Transcriptase that allows insertion into our genome for the rest of our lives
- Rev. Transcriptase takes +RNA to make ssDNA then dsDNA and back to +sssRNA (RT makes DNA from RNA)
- remember ssDNA cannot be transcribed –> cellular DNA Poly makes dsDNA and that is transcribed to mRNA
Ex. Retroviridae
Retroviridae
viral family in ss+RNA w/ DNA intermediate
Ex. HIV
ss (-) RNA
(-) RNA needs to be copied by viral RNA-dependent RNA Poly to +ssRNA
- NOT a host enzyme
Ex. Paramyxoviridae, Orthomyxoviridae, Filoviridae
- myxo = mucus
Paramyxoviridae
viral family in ss (-) RNA
causes measles
Orthomyxoviridae
viral family in ss (-) RNA
Ex. influenza virus, respiratory disease
Filoviridae
viral family in ss (-) RNA
ex. Ebola virus
- need to make +mRNA
- need viral RNA-dep RNA Poly (L protein)
