The microRNA pathway

Question 1

What are microRNAs (miRNAs)?

Answer 1

Endogenous activators of the RNAi pathway

miRNAs are small non-coding RNA molecules that regulate gene expression.

Question 2

Where are microRNA genes encoded?

Answer 2

Within the genome

Question 3

From what promoters are miRNAs typically expressed?

Answer 3

RNA polymerase II promoters

Question 4

What is the primary transcript of microRNA genes called?

Answer 4

primary microRNA (pri-miRNA)

Question 5

What structural features does pri-miRNA share with mRNA?

Answer 5

5’ cap and polyA tail

Question 6

What type of structures do pri-miRNAs form?

Answer 6

Hairpin-like structures

Question 7

What are the types of pri-miRNA based on the number of hairpins?

Answer 7

• Monocistronic
• Polycistronic

Question 8

What is released from pri-miRNA during nuclear processing?

Answer 8

70-80 nucleotide hairpins or pre-miRNA

Question 9

What complex processes pri-miRNA to pre-miRNA?

Answer 9

Microprocessor complex

Question 10

What are the components of the microprocessor complex?

Answer 10

• Drosha
• DGCR8

Question 11

What is the function of Drosha?

Answer 11

RNase III (dsRNA-specific endoribonuclease)

Question 12

What kind of overhang does Drosha create?

Answer 12

2 nucleotide, 3’ overhang

Question 13

What is the role of DGCR8?

Answer 13

dsRNA-binding partner of Drosha

Question 14

What is the homologous protein of DGCR8 in D. melanogaster/C. elegans?

Answer 14

Pasha (Partner of Drosha)

Question 15

How is pre-miRNA exported to the cytoplasm?

Answer 15

Via exportin-5

Question 16

What happens to pre-miRNA in the cytoplasm?

Answer 16

Undergoes a second processing step to form the miRNA duplex

Question 17

What is the size of the miRNA duplex?

Answer 17

20-25 bp

Question 18

What are the components involved in processing pre-miRNA to miRNA duplex?

Answer 18

• Dicer
• TRBP

Question 19

What is the function of Dicer?

Answer 19

RNase III

Question 20

What does TRBP stand for?

Answer 20

HIV trans-activating region RNA-binding protein

Question 21

What happens to the miRNA duplex after processing?

Answer 21

Enters RNA induced silencing complex (RISC)

Question 22

What strand of the miRNA duplex is removed in RISC?

Answer 22

Passenger/antiguide strand

Question 23

What determines the target specificity of the mature miRNA?

Answer 23

The sequence of the guide strand

Question 24

What type of base-pairing does miRNA use for target recognition?

Answer 24

Classical Watson-Crick base-pairing

Question 25

What occurs with a perfect match between miRNA and target mRNA?

Answer 25

RNA degradation

Question 26

What enzyme cleaves the target mRNA?

Answer 26

Argonaute-2 (Ago2)

Question 27

Where does Ago2 cleave target mRNA?

Answer 27

Between nucleotides 10 and 11 from the 5’ end of the guide sequence

Question 28

What occurs with an imperfect match between miRNA and target mRNA?

Answer 28

Translation suppression

Question 29

How many nucleotides are sufficient for target recognition?

Answer 29

As few as 7 nucleotides

Question 30

What is the seed region of miRNA?

Answer 30

Nucleotides 2-8 of guide

Question 31

What prevents Ago2 from cleaving mRNA when present?

Answer 31

Bulges between guide and target

Question 32

What are p-bodies?

Answer 32

Structures where mRNA is sequestered away from translational machinery

Question 33

What may bind to the 7-methylguanosine cap in p-bodies?

Answer 33

Preventing eIF4-E from binding