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MIMM 324 > 29. Retroviruses 1 > Flashcards

29. Retroviruses 1 Flashcards

1
Q

retrovirus replication

A
  1. RNA
  2. DNA
  3. integration into host genome
  4. viral protein production
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2
Q

general HIV replication cycle (10 steps)

A
  1. attachment
  2. fusion
  3. RT
  4. integration
  5. mRNA
  6. translation
  7. genome recognition
  8. assembly
  9. budding
  10. maturation
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3
Q

what is the role of Gag?

A

binds genomic RNA for genome recognition for assembly

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4
Q

what happens in acute infection?

A

1 billion particles are made, but not all are infectious bc of mistakes in splicing, transcription, translation, assembly, etc.

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5
Q

genome of retroviruses
- type
- size
- linear or circular
- segmented?
- haploid or diploid?

A
  • +ssRNA
  • 7-12kb
  • linear
  • non-segmented
  • diploid
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6
Q

family of retroviruses?

A

retroviridae

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7
Q

baltimore class of retroviruses?

A

group 6

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8
Q

size of virions

A

8-100nm diameter

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9
Q

hallmark of retroviruses

A

RT of viral RNA into linear dsDNA which is the reverse of the usual flow of genetic info

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10
Q

2 subfamilies of retroviridae

A
  1. orthoretrovirinae
  2. spumaretrovirinae
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11
Q

what is known about spumaretrovirus?

A

don’t cause disease

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12
Q

6 genera of orthoretrovirinae and the disease they cause

A
  1. alpharetrovirus –> RSV
  2. betaretrovirus –> mouse mammary tumour virus
  3. deltaretrovirus –> human T-cell leukemia virus
  4. epsilonretrovirus –> walleye dermal sarcoma virus
  5. gammaretrovirus –> murine leukemia virus
  6. lentivirus –> HIV
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13
Q

Which retroviruses are oncoretroviruses?

A

alpha, beta, delta, epsilon, gamma

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14
Q

how do lentiviruses cause disease?

A

killing or inducing loss of function in specific cells and tissues

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15
Q

organization of retroviral genome

A

3 ORFs

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16
Q

what are the 3 ORFs?

A
  1. Gag
  2. Pol
  3. Env
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17
Q

what proteins does Gag ORF make?

A

for structural proteins (matrix, capsid, nucleoprotein)

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18
Q

what is Gag cleaved by?

A

viral protease made in Pol ORF

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19
Q

what proteins does Pol ORF make?

A

viral enzymes (RT, integrase, protease)

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20
Q

what proteins does Env ORF make?

A

surface transmembrane components (viral envelope glycoproteins)

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21
Q

simple vs complex retroviruses

A

simple: gag, pol, env
complex: gag, pol, env, and auxillary + regulatory proteins

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22
Q

3 viral core proteins

A
  1. matrix/p17
  2. capsid/p24
  3. nucleocapsid/p7
23
Q

2 roles of matrix protein

A
  1. lines inner surface of viral envelope, linking it to viral core
  2. transport and binding of Gag to PM during assembly
24
Q

role of capsid protein

A

monomers dimerize and form capsid core which surrounds viral genome in mature virus for packaging

25
Q

role of nucleocapsid protein

A

monomers associate with 2 copies of viral ssRNA and package them into the viral core

26
Q

describe stability of capsid core and why this is a good target

A

weak interactions that can easily disassemble with drugs

27
Q

what is the capsid structure

A

200 copies of capsid monomers assembled in hexamers and pentamers, forming a CONE

28
Q

can molecules go thru capsid?

A

yes

29
Q

when do viruses encode an enzyme? (2)

A
  1. if there is no equivalent enzyme in the host to hijack
  2. if it is absolutely necessary for their life cycle
30
Q

3 virally encoded enzymes:

A
  1. RT
  2. integrase
  3. protease
31
Q

describe the RT

A

RNA-dependent DNA polymerase

32
Q

what is the issue with RT?

A

not reliable –> makes errors every time

33
Q

role of integrase

A

enables viral genomic material to be integrated within DNA of the cell

34
Q

role of protease in HIV

A

cleaves Gag into matrix, capsid, and nucleocapsid proteins

35
Q

what % of genome is retroviruses?

A

10%

36
Q

what are the 2 glycoproteins that HIV Env codes for?

A
  1. gp120
  2. gp41
37
Q

where is gp120 located?

A

extracellular

38
Q

where is gp41 located?

A

transmembrane

39
Q

what are the viral spikes made of?

A

trimer of gp120 and trimer of gp41

40
Q

describe how envelope glycoproteins determine the tropism of a virus

A

composition of glycoproteins depends on the retrovirus and determines the tissue and cell tropism of the virus bc they bind to cell-surface receptors

41
Q

what is required for transcription?

A

need elements at 5’ region for host transcription factors to bind –> otherwise virus will die

42
Q

how do retroviruses get multiple transcripts from 1 DNA?

A

splicing

43
Q

OVERALL REPLICATION CYCLE (9 steps)

A
  1. glycoproteins bind cell receptors
  2. virus and cell membranes fuse and viral core enters cytoplasm
  3. in the viral core, RNA is transcribed into DNA by RT
  4. dsDNA is translocated to nucleus for integration via integrase to form provirus
  5. provirus is transcribed forming spliced and unspliced mRNA and full-length RNA genomes
  6. viral mRNAs are translated
  7. proteins and genomic RNA traffic to PM for assembly
  8. particle buds from PM, acquiring envelope
  9. virus matures after budding by proteolytic cleavage of Gag and Gag/Pol polyproteins
44
Q

3 ways that retroviruses have oncogenic potential

A
  1. viral genes encode proteins that drive cell into uncontrolled proliferation
  2. viral genome integrates adjacent to cellular proto-oncogenes and viral LTR stimulates expression of oncogene (insertional mutagenesis)
  3. viral gene encodes protein that binds and transactivates host cellular genes to dysregulate cell cycle
45
Q

example of viral gene encoding proteins that drive uncontrolled proliferation

A

Src in RSV –> first oncogene discovered

46
Q

function of Src

A

tyrosine kinase that phosphorylates targets involved in cell cycle regulation and proliferation to cause uncontrolled cell growth

47
Q

role of Src in virulence

A

Src is not required for viral survival but greatly enhances virulence

48
Q

example of insertional mutagenesis

A

mouse mammary tumour virus

49
Q

how does mouse mammary tumour virus work?

A

produces tumours by inserting genomes into critical sites near/within proto-oncogene –> causing production of active oncogene

50
Q

example of transactivation of viral and cellular genes

A

Tax gene in HTLV-1 activates transcription of viral HTLV-1 proteins and human genes involved in cell cycle regulation –> causes adult T-cell leukemia

51
Q

what are endogenous retroviruses?

A

genetic elements found ubiquitously in eukaryotic DNA

52
Q

what do endogenous retroviruses do?

A

amplify themselves to an RNA intermediate and uses RT + integrase to paste themselves randomly in the genome

53
Q

2 uses of retroviruses in the biotech industry

A
  1. RT-PCR
  2. Lentiviruses as vectors for targeted gene therapy
  3. Lentivirues as vectors for Cas9

MIMM 324 (37 decks)

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