RNA interference (RNAi) and microRNAs

Post Transcriptional, Transcriptional gene Silencing

RNA interference (RNAi): silencing of genes by complementary dsRNA via 2 ways

Post Transcriptional

dsRNA leads to degradation of complementary mRNA - also known as Gene Silencing (PTQS)

Transcriptional gene Silencing

dsRNA also leads to transcriptional silencing the complementary gene

RNA interference Step 1

Enzyme Dicer recognizes dsRNA and cleaves it into 21-25 bp fragments - called small interfering RNAs (siRNAs)

RNA interference Step 2

RNA-induced silencing complex (RISC) binds and denatures the double-stranded RNAs into single 21-25 bp strands

• One RNA strand is identified by RISC as the guide strand (the other strand known as passenger strand is degraded)

RNA interference Step 3

The guide strand-RISC complex uses complementary base pairing to recognize mRNA

• The key enzymatic component of RISC is Argonaute

  
  

RNA interference Step 4

mRNA- siRNA- RISC complex cleaves mRNA at the places of siRNA-mRNA complementation, leading to mRNA degradation RNA interference - process and enzymes

RNA interference - Transcriptional Silencing

• Innate defense mechanism against RNA viruses

• RNAi via RISC results in mRNA degradation

  
  

siRNA made by Dicer is bound by another complex

RNA-induced Transcriptional Silencing RITS

RNA-induced Transcriptional Silencing RITS

• Binds to DNA of endogenous gene

• Recruit histone methyltransferases that put on H3K9Me3 to silence the gene and form

• heterochromatin = transcriptional repression