The presence of the bromo substituent allows the base to mispair with guanine via the enol tautomer

TLS Online TPP Program

#Id: 6802

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6803

#Unit 3. Fundamental Processes

The base pairing between miRNA and target RNA is initiated by interactions of so-called seed residues—typically the sequence between bases 2 and 9 of the 22-nucleotide miRNA

TLS Online TPP Program

#Id: 6804

#Unit 3. Fundamental Processes

Humans express four Argonaute proteins. AGO2 is the human Argonaute protein in miRNA-containing RISC complexes.

TLS Online TPP Program

#Id: 6805

#Unit 3. Fundamental Processes

AGO2 is the protein responsible for the cleavage of targetRNA. One domain of the protein is homologous to theRNase H enzymes that degrade the RNA of an RNA-DNA

hybrid

TLS Online TPP Program

#Id: 6806

#Unit 3. Fundamental Processes

When the 5′ end of the siRNA of a RISC complex base-pairs precisely with a target mRNA over a distance of one turn of an RNA helix (10–12 base pairs), this domain of AGO2 cleaves the phosphodiester bond of the target RNA across from nucleotides 10 and 11 of the siRNA

TLS Online TPP Program

#Id: 6807

#Unit 3. Fundamental Processes

The precursor RNA for the siRNA pathway is a longer dsRNA. As a consequence of this different initial substrate, Drosha is not needed for the generation of siRNAs. Cleavage by Dicer is still required, however, and again generates a suitable 21- to 22-nucleotide RNA for incorporation into RISC.