Mechanism of rna interference
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Transcript of Mechanism of rna interference
The process by which RNAi occurs in different organisms varies slightly ; This is usually because different proteins are used in the process of RNAi .
The Mechanism of RNA Interference
4
Differencesbetween siRNA and
microRNA miRNA: ssRNA 19-25nt. In nucleus MicroRNAs
predominantly suppress the translation of mRNA targets,
siRNA:• dsRNA 21-22 nt.• In sytoplasm• siRNAs prevent
mRNA translation and lead to mRNA degradation, also involved in the regulation of gene expression at the transcriptional level
RISC
• RISC:RNA-inducing silencing complex • The siRNAs are incorporated into the (RISC) which consists of an Argonaute (Ago) protein components. • Argonaute protein is considered catalytic engine • Ago cuts mRNA targets guided by siRNA via its endonuclease nicknamed“ slicer”.
DICER & Drosha
dsRNAs are cleaved into 21-23 nt segments siRNAs by an enzyme called "Dicer" Drosha : cleaves base hairpin in to form pre miRNA; which is later processed by Dicer
RNAi Mechanism 4 major steps:• dsRNA is cleaved into siRNA• The siRNA association with RISC,
unwinding & activation of RISC• Association with target mRNA• Degradation of mRNA
STEP 1• dsRNA is
processed into sense and antisense RNAs • 21-25 nucleotides in
length • have 2-3 nt 3’
overhanging ends • Done by Dicer (an
RNase III-type enzyme)
Step 3
• the antisense siRNAs act as guides for RISC to associate with complimentary single-stranded mRNAs.
Step 4
• RISC cuts the mRNA approximately in the middle of the region paired with the siRNA
• The mRNA is degraded further