5 - Small RNAs in the regulation of biological processes Flashcards
Give a general overview of RNAi (RNA interference)
dsRNA is used to produce siRNA, which inhibits RNA that the dsRNA is derived from
siRNA = small interfering RNA
Where is dsRNA derived from?
viruses
Give the order of events for RNAi
- DICER breaks up RNA into fragments
- passenger strand is removed
- RISC complexes formed
What is DICER?
an Rnase III like endonuclease activity
How is the passenger strand removed in step 2 of RNAi?
i.e.
What kind of activity allows for the removal of the strand?
What proteins are required?
What is the remaining strand?
(the passenger strand is one of the siRNA strand) It is siRNA guided endonuclease activity that removes the strand. Requires AGO (argonauts-piwi proteins) The strand that remains is antisense to the target strand)
What is the RISC complex?
RNA-induced silencing complex
they associate with the ssRNA
What do the RISC complexes do?
They recognise and cleave target mRNA molecules (which have complementary sequences to the incorporated single-stranded guide siRNA)
What is siRNA used as therapy for?
to prevent cell division and to turn off genes that we don’t want to express
What is shRNA?
small hairpin RNA
When siRNA is synthesised artificially, it can more (more conveniently) synthesised as one long strand which folds pack on itself
What is gene knockdown?
decreasing the amount of proteins produced from a gene
siRNA vs miRNA
siRNA - inhibit the expression of one specific target mRNA
miRNA - regulate the expression of multiple mRNAs.
A considerable body of literature now classifies miRNAs as RNAi molecules
What is the seed region?
most important region for miRNA targeting
lies between nucleotide position 2 and 8 from 5’ end and is often flanked by adenosines
Where are the majority of the miRNA target sites?
within 3’ UTRs and the seed region
