Virology test 1 lecture 7 Flashcards

2/07

• not infectious by self
• RdRp is INSIDE the viron, bc needed for transcription to be done upon entering cell
• transcription/translation
  • RdRp used to make mRNA from (-) strand viral RNA
  • once transcribed, can translate mRNA -> single proteins (NOT polyproteins)
• replication
  • makes fullsized (+) RNA (NOT mRNA) intermediate, but is NOT translated
  • instead, use (+) RNA as template to make more (-) RNA
    
    

notes

(-) rna viruses

- their genomes are opposite polarity of mRNA

- NOT directly infective

– use RNA dependent RNA polymerase that they carry in their virion

- enables them to make mRNA from their genome ( - RNA -> mRNA )

Monocystronic -> made into single proteins

Replication of negative strand requires full size (+) RNA intermediate to create more negative strand

- (+) intermediate used to make (-) RNA, so makes a strand of the original polarity

monocystronic proteins (make single proteins, not polyproteins)

mRNA

• shorter than genome template + RNA
• contains 3' poly A tail
• contains 5' cap

antigenomic (+) RNA

• exact copy of template genome
• no 3' poly A tail
• no 5' cap

single (nonsegmented) genome

• measles
• mumps
• rapies
• VSV
• RSV

segmented genome

• influenza

transc/trans

- strand RNA -> transcription -> monocystic mRNAs -> translation = proteins

replication

• (-) strand RNA vgenome -> make (+) strand RNA template -> make (-) strand progeny RNA

proteins + (-) progeny RNA = progeny virus

for either:

• virus (-) RNA bind receptor
• -> viral membrane fuse cell membrane
• then viral polymerase is in capsid
  • transcription or replication

newly made nucleocapsids associated w/ matrix and glycoprotein - modified plasma membrane = enveloped virus

cytoplasm (except flu)

budding

bc the proteins assoiciate w/ matrix and glycoprotein modified plasma

(-) RNA

• transcription
  • virion RNA pol respect initiation-termination signals
  • = generate individual mRNAs for each protein
• replication
  • virion RNA pol will not stop in transcription recognition signals
  • = generate full-length (+) RNA indermediate template = NOT mRNA

can swtch between transcription/replication mode

(-) genome released in cell

• Transcription mode
• Then either go down replication or translation route
  • Either made template (+) RNA or mRNA depending which it is doing

• allows for reassortment to occur
  • = good for viral pathogenicity (can only do reassortment if segmented)
• diff gene segments encode diff proteins
• transcription
  • viral RNA polymerase generate mRNAs from each genomic segment
  • each segment contains its own signals to initiate transcription
• replication
  • viral RNA pol will generate (+) RNA intermediates from each genome segment which will be copied into (-) RNA genomes

pretty much same thing as nonsegmented

segmented (-) strand RNA virus

• replicates in host cell nucleus (this virus is the EXCEPTION)
• replicate in nucleus bc flu transcriptase use host cell 5' cap mRNA as a PRIMER for viral mRNA synthesis

consequence: viral endonuclease PB2 cuts cell's mRNA 5' cap structure as well as 10-13 nucleotides from cellular mRNA

• = capped RNA oligonucleotides function as primer for transcription initiation
• = disabling host cell protein synthesis

it replicates in the host nucleus because the mRNA's 5' cap structure is required to work as the virus' primer for transcription

= host cell cannot make any more proteins

• naked - double capsid
• most - segmented genomes
• mRNA made only from one template strand of each segment
  • uses (-) strand template!!! (-> so make (+) RNA = mRNA)
• transcription
  • similar to ds DNA genome -> (-) strand template
• necessary enzymes must be encoded, packaged in virion + carried to next cell
• after infection initiation -> several proteins in virion particle removed by protease in intestinal tract -> form intermediate/infectious subviral particle
  • this is the functional particle
  • virus must become activated by GI tract - if not, gets deactivated
  • virus ingested, activated by protease in GI tract
• DS GENOME - in ISVP
  • but viral mRNA is in cytoplasm outside the ISVP

conservative replication

penetrate the cell

receptor mediated endocytosis

• The viral particle that has been activated by the GI tract protease which allows it to become functional and do its work in the cell upon entering
• releases core into cytoplasm
• enzymes in the core initiate mRNA production
• each (-) strand use as template by virion core enzymes
  • individual mRNAs made and mRNAs leave core to be translated
• later, virion proteins and (+) RNA segmentes form cores
  • (+) RNA copied to make (-) RNA in cores = ds genome

• enveloped SS genome
• capsid w/ 2 identical copies of (+) strand mRNA genome
• copies of reverse transcriptase (RT) and integrase
• has 2 tRNAs - used as primers
• mRNA genome is NOT infectious bc does not encode RdRp
• encode RNA dependent DNA polymerase and replicate thru dna intermediate
• contradicted central dogma bc shows RNA can -> produce DNA (backwards)
• important in humans bc responsible for
  • HIV
  • HTLV-I
• important for studied/technology
  • gave rise to enzyme used for PCR

2 (+) strand RNAs

1 RNA -> give rise to cDNA strand (reverse transcriptase)

-> remaining RNA strand degraded

-> use cDNA to create complementary cDNA using DNA-depdendent DNA polymerase from host cell

-> integrate into cellular host genome

(make sure these steps are correct)

notes

Starts w/ 2 (+) strands

One + strand RNA -> make ss DNA strand using RT

Then next RNA -> ss DNA using RT

So now have ds DNA

-> nucleus

not sure

maybe it increases probability of successful DNA synthesis bc if one is broken, RT can switch templated + copy the RNA = DNA synthesis

3 major genes

• gag -> capsid proteins
• pol -> polymerase, protease, integrase
• env (envelope) -> glycoproteins

end of each RT genome = long terminal repeat sequence (LTR)

LTRs -> contain promoters, enhancers and other gene sequences used for binding of diff transcription factors

oncogenic retroviruses -> contain oncogenes

complex retroviruses (HTLV) -> encode other regulatory proteins

viral attachment to receptor/coreceptors (CCR5 and CXCR4) necessary for infection

attach CD4 (Helper T) cells exclusively

if someone does not have receptor -> they are resistance to infection

• RT use virion tRNA as primer + make complementary (-) strand DNA (cDNA)
• RT act as ribonuclease H
  • degrade RNA genome left + make (+) strand DNA
• during synth of provirus, sequences from each end of genome are duplicated = attach the LTRs to both ends
• process creates sequences necessary for integration + makes enhancer and promoter regions in the LTRs for transcription regulation
• ds DNA delivered to nucleus + integrated into host chromosome

• viral DNA transcribed (in the cell's genome) by the host's RNA pol II
• = full length RNA
  • can either:
    • proceed to make
      • mRNA
      • translation = proteins
    • assemble into new virions

RT OCCURS WITHOUT FULL UNCOATING OF THE GENOME

Nucleocapsid partially dissolved

WHICH EXPLAINS WHY THE GENOME (mRNA) IS NEVER TRANSLATED

(thus not full genome is used)

• extent of methylation of viral DNA
• cell's growth rate
• ability of cell to activate enhancers + promoters encoded in the lTR

stimulation of the cell by mitogens, certain lymphokines, or infection of the cell w/ exogenous viruses produces transcription factors which bind LTR + activate viral transcription

viral oncogenes promote cell proliferation = stimulate transcription and viral replication