Chapter 13

Question 1

The basic structure of togavirus

Answer 1

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

Question 2

E1/E2 form

Answer 2

dimer

Question 3

envelope protein has same T due to

Answer 3

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

Question 4

Sindbis virus (Alphavirus)

Answer 4

Birds and mosquitoes

Question 5

Semliki forest virus (Alphavirus)

Answer 5

Birds, rodents, primates and mosquitoes

Question 6

Rubella virus (Rubivirus)

Answer 6

Humans

Question 7

Common symptoms of togaviruses are

Answer 7

rash, fever, joint pain, encephalitis

Question 8

alphaviruses can infect humans, and rubella is known as

Answer 8

german measles

Question 9

children are given with mixed vaccine for

Answer 9

measles, mumps and rubella

Question 10

the genome structure of the togavirus is

Answer 10

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

Question 11

there are 2 ORFs

Answer 11

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

Question 12

NS polyprotein is translated from

Answer 12

genome

Question 13

NS polyprotein has a readthrough

Answer 13

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

Question 14

S polyprotein is translated from

Answer 14

sg mRNA

Question 15

PE2 of S polyprotein makes

Answer 15

E3 and E2

Question 16

E2 is

Answer 16

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

Question 17

Cell entry is by

Answer 17

receptor-mediated endocytosis

Question 18

NC release is by

Answer 18

pH-dependent fusion by E1

Question 19

E1/E2 trimer becomes

Answer 19

E1-only trimer for NC release

Question 20

uncoating occurs as

Answer 20

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

Question 21

NS proteins at 5’ ORF are translated

Answer 21

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

Question 22

Sindbis virus NS proteins are

Answer 22

nsP1, nsP2, nsP3, nsP4

Question 23

nsP1 is

Answer 23

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

Question 24

nsP2 is

Answer 24

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

Question 25

nsP3 has

Answer 25

unknown function. phosphorylated at Thr and Ser residues

Question 26

nsP4 is

Answer 26

RNA polymerase. Unstable, degraded by ubiquitin pathway

Question 27

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

Answer 27

P1234 and P123

Question 28

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

Answer 28

nsP4 available to replicate the (-)-strand RNA

Question 29

P123/nsP4 complex is

Answer 29

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

Question 30

the complex nsP1,nsP2,nsP3,nsP4 is

Answer 30

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

Question 31

when enough P123 copies are made, trans-cleavage generates

Answer 31

nsP1, P23, and finally nsP2 and nsP3

Question 32

the ratio between sg and g RNAs is

Answer 32

10:1 for higher structural proteins to be transcribed

Question 33

the sg RNA has ends of

Answer 33

5' internal and 3' coterminal

Question 34

Sindbis virus S proteins are translated

Answer 34

later from sg mRNA, carrying out virion assembly

Question 35

Sindbis virus S proteins are

Answer 35

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

Question 36

Capsid protein is

Answer 36

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

Question 37

PE2 is

Answer 37

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

Question 38

E3 is

Answer 38

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

Question 39

E2 is

Answer 39

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.

Question 40

6K is

Answer 40

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

Question 41

E1 is

Answer 41

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

Question 42

RNA and capsid translated are processed in

Answer 42

the cytoplasm

Question 43

envelop proteins are fed through

Answer 43

the ER membrane

Question 44

proteins in the lumen are

Answer 44

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

Question 45

proteins in the cytosol are

Answer 45

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

Question 46

in the trans-Golgi vesicle,

Answer 46

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

Question 47

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

Answer 47

located and bud out as a virion

Question 48

in the alphavirus expression vectors, viral genomes are

Answer 48

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

Question 49

alphavirus expression vectors are non-cytopathic due to

Answer 49

single amino acid change in C-terminus of nsP2

Question 50

the replicon has no

Answer 50

structural genes

Question 51

alphavirus expression vectors are complement with

Answer 51

"helper virus", providing structural genes.

Question 52

Helper virus being inactivated with packaging signal is

Answer 52

suicidal, only allowing replicon to be packaged

Question 53

double subgenomic RNA vector has 2 sg mRNAs:

Answer 53

structural protein genes and foreign genes

Question 54

double sg RNA vector is used for

Answer 54

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

Question 55

classical genetics focused on

Answer 55

phenotype to genotype

Question 56

reverse genetics focuses on

Answer 56

genotype to phenotype

Question 57

as an example of reverse genetics,

Answer 57

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