Ch. 10 Processing of Viral Pre-mRNA

Question 1

Why is RNA processing needed?

Answer 1

It is needed for recognition by the protein synthesizing machinery and translation by cellular ribosomes.

Question 2

What are two of the important RNA modifications?

Answer 2

5’ capping and 3’ polyadenylation.

Question 3

How can translation be regulated

Answer 3

Small RNA’s can bind to mRNA in cytoplasm leading to RNA silencing/interference

Question 4

Virtually all cellular and viral mRNA possess the same cap structure. What is it?

Answer 4

m7GpppN, where N is any nucleotide. (7 methyl guanosine triphosphate)

Question 5

What are the three mechanisms in which mRNA can be capped?

Answer 5

De novo synthesis by cellular enzymes; synthesis by viral enzymes; “cap stealing” by acquisition from cellular pre-mRNA’s.

Question 6

What stabilizes the 5’ cap?

Answer 6

Methylization of 2’ OH group on ribose or terminal guanosine

Question 7

Cellular and viral polymerases methylate differently. Cellular pol methylates ____ cap addition and viral pol methylates ____ 5’ cap addition

Answer 7

After, before

Question 8

Formation of cap structure by cellular pol occurs when the nucleotide is _____ nucleotides long.

Answer 8

20-30

Question 9

How does the cell signal RNA Pol II to bind?

Answer 9

Phosphorylation of C-term domain of large subunit

Question 10

What proteins do the capping enzymes have?

Answer 10

5’ Triphosphatase; Guanylyltransferase

Question 11

When is it necessary for viral enzyme synthesis of a 5’ cap?

Answer 11

When mRNA is synthesized in the cytoplasm (cellular machinery in nucleus)

Question 12

What are viral capping enzymes associated with? What was one of the first viruses where this was discovered?

Answer 12

RNA Pol; Vaccinia virus

Question 13

How does cap snatching work? Which viruses use this method?

Answer 13

Cap snatching works by the cap and 10 to 13 nucleotides. A G protein peptide bonded to the (-) RNA is incorporated into the cap primer, and then the strand is elongated. Bunyavirus, orthomyxovirus

Question 14

What is the purpose of the 3’ Poly (A) tail? What do mRNA lacking a tail do to prevent nucleolytic attack?

Answer 14

Serves to stabilize mRNA and increase translation efficiency.
They form a stem loop structure

Question 15

Cellular poly adenylation: What is the nucleotide sequence recognized by Cpsf (cleavage and polyadenylation specificity protein)?

Answer 15

5’-AAUAAA-3’

Question 16

Cellular poly adenylation: What occurs after Cpsf cleaves the end of mRNA?

Answer 16

Poly (A) pol attaches and adds 10-15 A residues. Other proteins stabilize it and it adds a total of 200 A residues

Question 17

Viral poly adenylation: Capping protein-RNA Pol II complex stay together until reaching termination signal. What happens next?

Answer 17

Viral Poly (A) Pol adds Poly (A)

Question 18

What is pre-spliced mRNA called? Do they have a 5’ Cap and Poly A tail? What happens to the sequences immediately adjacent to these features?

Answer 18

heterogenous nuclear RNA;
YES;
They are conserved in mature mRNA.

Question 19

What are the nucleotide sequences found at the ends of almost all introns?

Answer 19

GU and AG.

Question 20

What type of reaction eliminates introns? What is the product of the first? the second?

Answer 20

two trans-esterification reactions; One 5’ exon and one intron-3’ exon complex; two attached exons and one intron

Question 21

What is a spliceosome comprised of?

Answer 21

Many proteins and 5 small nuclear (snRNA’s) U1,U2,U4, U5, and U6

Question 22

What is Constitutive splcing?

Answer 22

Splicing where all exons are conserved.

Question 23

What is Alternative splicing?

Answer 23

splicing of different combinations of exons.

Question 24

How is viral mRNA edited?

Answer 24

By the insertion of nucleotides not specified in the template or the alteration of a base

Question 25

What is one possible purpose of mRNA editing?

Answer 25

It can convert a UAG (stop codon) to something else in order to code two proteins with less genomic information. Converts stop to UGG (Tryp) in Hepatitis Satellite Delta virus

Question 26

What are some methods of mRNA exportation from the nucleus?

Answer 26

Binding with Rev(ribonucleoprotein that shuttles between nucleus and cytoplasm)

Question 27

Slide 27

Answer 27

if you have time

Question 28

What are small interfering RNAs (siRNAs)? How are they made?

Answer 28

They are small RNA molecules that induce mRNA degradation or inhibit translation. They are made by endonucleolytic cleavage of dsRNAs by cytoplasmic dicer enzymes