CSB349H1 Lecture Notes - Lecture 11: Antisense Rna, Small Interfering Rna, Piwi
Lecture 11(a): miRNA, RNAi & ncRNA:
RNA Interference (RNAi):
• Antisense-Inhibition:
o Injecting single-stranded antisense RNA to hybridize with the target mRNA and
silence its effects (mild silencing)
ð Injecting double-stranded RNA (sense & antisense) led to the complete degradation of
mRNA that contained the same sequence of the double-stranded RNA, therefore had a
much stronger silencing effect
o Long double-stranded RNA is processed into short interfering RNA (siRNA)
§ Dicer and AGO are important in processing siRNA
Micro RNA (miRNA):
• Small RNA are coded within the genome and often come as precursor miRNA via Drosha
o Precursors are then processed by Dicer to give rise to mature miRNA
• miRNAs can have one or several targets:
o Hybridization of miRNA to 3’ UTR is not always perfect:
§ Base-Pair Mismatch: leads to translation inhibition
§ Perfect Base-Pairing: leads to target cleavage
ð miRNA do not require perfect-base pairing to function; they are capable of mismatching to
target several mRNAs – they will bind to the 3’ UTR of mRNA and form an RNA-Induced
Silencing Complex (RISC) which can inhibit translation or transport them to P-bodies
miRNA versus siRNA:
• Both are short in length however differ in their mode of action and origin
a) miRNA:
§ Encoded in the genome
§ Does not require perfect binding to target – silencing mRNA translation
b) siRNA:
§ Defense mechanism against invading nucleic acids
§ Requires perfect hybridization – cleaves mRNA target
Document Summary
Rna interference (rnai): antisense-inhibition, injecting single-stranded antisense rna to hybridize with the target mrna and silence its effects (mild silencing) Dicer and ago are important in processing sirna. Mirna do not require perfect-base pairing to function; they are capable of mismatching to target several mrnas they will bind to the 3" utr of mrna and form an rna-induced. Silencing complex (risc) which can inhibit translation or transport them to p-bodies mirna versus sirna: both are short in length however differ in their mode of action and origin, mirna: Does not require perfect binding to target silencing mrna translation: sirna: Sense strand: known as the passenger strand (mirna*) Guide strand of sirna assembles into the risc to form an rna-protein complex (sirisc) that binds to the target mrna and silence gene expression by cleaving the target rna. Risc complex: risc components include: dicer, argonaute (ago) and various rna binding proteins, ago proteins: