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BIOL 3155 > Chapter 13 > Flashcards

Chapter 13 Flashcards

Togavirus

1
Q

The basic structure of togavirus

A

enveloped icosahedral with T=4 capsid, (+) ss-RNA with 1 capsid protein and 4 enveloped protein (E1, 2, 3, 6K)

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2
Q

E1/E2 form

A

dimer

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3
Q

envelope protein has same T due to

A

transmembrane and helix that affix with capsid protein through lipid bilayer membrane

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4
Q

Sindbis virus (Alphavirus)

A

Birds and mosquitoes

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5
Q

Semliki forest virus (Alphavirus)

A

Birds, rodents, primates and mosquitoes

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6
Q

Rubella virus (Rubivirus)

A

Humans

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7
Q

Common symptoms of togaviruses are

A

rash, fever, joint pain, encephalitis

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8
Q

alphaviruses can infect humans, and rubella is known as

A

german measles

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9
Q

children are given with mixed vaccine for

A

measles, mumps and rubella

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10
Q

the genome structure of the togavirus is

A

linear (+) ss-RNA with 5’ cap structure and 3’ poly(A) tail

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11
Q

there are 2 ORFs

A

one with 1 NS polyprotein that makes 4 mature proteins; one with 1 S polyprotein that makes 5 mature proteins

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12
Q

NS polyprotein is translated from

A

genome

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13
Q

NS polyprotein has a readthrough

A

between nsP3 and nsP4 with UGA, and end at the downstream of nsP4 with UAG

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14
Q

S polyprotein is translated from

A

sg mRNA

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15
Q

PE2 of S polyprotein makes

A

E3 and E2

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16
Q

E2 is

A

an attachment protein that interact with laminin receptor (SinV receptor)

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17
Q

Cell entry is by

A

receptor-mediated endocytosis

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18
Q

NC release is by

A

pH-dependent fusion by E1

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19
Q

E1/E2 trimer becomes

A

E1-only trimer for NC release

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20
Q

uncoating occurs as

A

60S ribo subunit binds capsid and destabilizes it, releasing RNA genome into the cytosol

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21
Q

NS proteins at 5’ ORF are translated

A

first from genome, carrying out genome replication and sg mRNA transcription

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22
Q

Sindbis virus NS proteins are

A

nsP1, nsP2, nsP3, nsP4

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23
Q

nsP1 is

A

RNA capping enzyme; has methyltransferase activity. required for initiation of transcription of (-)-strand RNA and modulation of nsP2 protease activity.

24
Q

nsP2 is

A

cysteine proteinase, RNA helicase. required for synthesis of subgenomic RNA. mutation in nsP2 show reduced cytopathic effects and lower shutoff of host cell protein synthesis

25
Q

nsP3 has

A

unknown function. phosphorylated at Thr and Ser residues

26
Q

nsP4 is

A

RNA polymerase. Unstable, degraded by ubiquitin pathway

27
Q

translation and readthrough from (+)-strand RNA at 5’ cap make

A

P1234 and P123

28
Q

cis-cleavage at 3/4 site of P1234 with nsP2 make

A

nsP4 available to replicate the (-)-strand RNA

29
Q

P123/nsP4 complex is

A

replicating the (+)-strand RNA from 3’ to 5’, making (-)-strand RNA

30
Q

the complex nsP1,nsP2,nsP3,nsP4 is

A

replicating the (-)-strand RNA from 3’ to 5’, making (+)-strand RNA and (+)-strand sg RNA from two different promoters

31
Q

when enough P123 copies are made, trans-cleavage generates

A

nsP1, P23, and finally nsP2 and nsP3

32
Q

the ratio between sg and g RNAs is

A

10:1 for higher structural proteins to be transcribed

33
Q

the sg RNA has ends of

A

5’ internal and 3’ coterminal

34
Q

Sindbis virus S proteins are translated

A

later from sg mRNA, carrying out virion assembly

35
Q

Sindbis virus S proteins are

A

Capsid, PE2 -> E3 and E2, 6K, E1

36
Q

Capsid protein is

A

forming nucleocapsid; contains serine-like protease that autocatalytically cleaves itself from the polyprotein.binds to genome RNA packaging signal via positively charged amino terminus

37
Q

PE2 is

A

precursor to E2. cleaved in trans-Golgi vesicles by a furin-like cellular protease; rarely incorporated into virions

38
Q

E3 is

A

Amino-terminal part of PE2 containing the signal sequence. glycosylated; retained in virions of Semliki Forest but not Sindbis virus

39
Q

E2 is

A

carboxy-terminal part of PE2, a component of virus envelope projections. C-terminal cytoplasmic domain binds to capsid during assembly. binds to cellular receptors; contains epitopes for neutralizing antibodies. palmitoylated.

40
Q

6K is

A

membrane associated; palmitoylated; C-terminus is signal sequence for E1. Small amounts in virions; enhances virus assembly and budding, possible role in hydrogen ion transport

41
Q

E1 is

A

component of virion envelope projections; type 1 transmembrane glycoprotein with two positively charged C-terminal amino acids in the cyotoplasm; palmitoylated and glycosylated; functions in low-pH activated membrane fusion

42
Q

RNA and capsid translated are processed in

A

the cytoplasm

43
Q

envelop proteins are fed through

A

the ER membrane

44
Q

proteins in the lumen are

A

E1 (cellular signal peptidase E1/6K)
E2 (cellular signal peptidase 6K/pE2)
E3 (furin protease pE2/E3)

45
Q

proteins in the cytosol are

A

6K, some of E2, some of E3, capsid (cis-clv E3/C)

46
Q

in the trans-Golgi vesicle,

A

palmitolyation of E3 region and glycosylation of E2 region and cleavage of pE2. E1-E2 dimer formation.

47
Q

fusion occurs on the plasma membrane, the nucleocapsid with RNA is

A

located and bud out as a virion

48
Q

in the alphavirus expression vectors, viral genomes are

A

modified by foreign gene in the S protein region, allowing for expression of heterologous proteins

49
Q

alphavirus expression vectors are non-cytopathic due to

A

single amino acid change in C-terminus of nsP2

50
Q

the replicon has no

A

structural genes

51
Q

alphavirus expression vectors are complement with

A

“helper virus”, providing structural genes.

52
Q

Helper virus being inactivated with packaging signal is

A

suicidal, only allowing replicon to be packaged

53
Q

double subgenomic RNA vector has 2 sg mRNAs:

A

structural protein genes and foreign genes

54
Q

double sg RNA vector is used for

A

expressing high levels of a protein for experimental study or vaccines, and is a potential for insectices

55
Q

classical genetics focused on

A

phenotype to genotype

56
Q

reverse genetics focuses on

A

genotype to phenotype

57
Q

as an example of reverse genetics,

A

viral genomes are replicated as DNA strain, then inserted into the DNA plasmid to observe a particular protein function.

BIOL 3155 (16 decks)

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