RNA Interference Pathways and Therapeutic Exploitation - RNA Interference from Biology to Therapeutics - page 4

Genomic DNA

1

Pri-miRNA

Dr osha DG C R8

2

Long dsRNA

Pre-miRNA

XPO5

4

3

4

RLC

RLC

Dicer

TRBP

Dic er

TRBP

Ago

Ago

5

5

pre-RISC

pre-RISC

Ago

TRBP Ago TRBP

Dicer

Dicer

6

6

RISC

Ago

7 8

ORF

AAAA

AAAA

Ago1-4 Ago2

Target cleavage

Target destabilisation

mRNA destabilisation /
translational inhibition

1
2

4 Uptake into RLC
5

7

Transcription by Pol-II

Dicer cleavage

Microprocessor cleavage

8 Ago2-mediated cleavage

3 Nuclear export by XPO5 6 RISC activation

Fig. 1.1 Overview of the RNAi pathways. Natural miRNAs are transcribed by pol II as part of
long pri-miRNAs j , which are processed in the nucleus ( gray circle ) by the microprocessor (con-
taining DGCR8 and Drosha) into pre-miRNAs k . These are subsequently exported to the cyto-
plasm by XPO5 l and loaded into a RISC-loading complex (RLC) containing, e.g., Dicer and
TRBP m . In the cytoplasm, Dicer cleaves the pre-miRNA ( left ) and cytoplasmic long dsRNA
( right ) into a miRNA or siRNA duplex, respectively n , thereby generating pre-RISC in which one
strand is selectively loaded into active RISC o . RISC can now direct mRNA destabilization/trans-
lational inhibition of target sharing only partial sequence complementarity to the guiding strand p
(typical for miRNAs) or RNA cleavage of targets sharing perfect sequence complementarity to
guide strand q (typical for siRNAs). SiRNAs generated from cytoplasmic long dsRNA can, due
to their perfect sequence identity, target their original source, e.g., viral dsRNA for degradation
( dashed line ). Refer to text for more detailed description