5 - Small RNAs in the regulation of biological processes. Flashcards
Argonaute
Argonaute proteins are the catalytic components of the RNA-induced silencing complex (RISC).
DICER
Dicer is an endoribonuclease that cleaves doublestranded RNAs (dsRNAs) and pre-microRNAs (miRNAs) into short double-stranded RNA fragments (20-25 nucleotides), with a two-base overhang at the 3′ end. Dicer facilitates the formation of the RNA-induced silencing complex (RISC).
Drosha
Drosha is the RNAse responsible for initiating the processing of microRNA (miRNA), or short RNA molecules from their Pri-miRNA precursor transcripts. Drosha enzyme is localised in the cell nucleus.
Long non-coding RNA (long ncRNA)
Long ncRNAs are nonprotein coding transcripts longer than 200 nucleotides. As a class, long ncRNAs have been found to have diverse regulatory functions, including the regulation of gene transcription, post transcriptional gene regulation, regulation of protein translation, epigenetic gene regulation, genomic imprinting and Xchromosome inactivation.
microRNA (miRNA)
miRNAs are small non-coding RNA molecules (around 22 nucleotides in size) found in plants and animals, which function in the transcriptional and posttranscriptional regulation of gene expression. By affecting gene regulation, miRNAs are likely to be involved in most biological processes.
Non–coding RNA (ncRNA)
A functional RNA molecule that is not translated into a protein. Non-coding RNAs include highly abundant and functionally important RNAs such as transfer RNA (tRNA) and ribosomal RNA (rRNA), as well as RNAs such as microRNAs, siRNAs, snRNAs,, piRNAs and the long ncRNAs.
Piwi-interacting RNA (piRNA)
piRNAs are the largest class of small non-coding RNA molecules expressed in animal cells and form RNA-protein complexes through interactions with piwi proteins. These piRNA complexes have been linked to epigenetic and post-transcriptional gene silencing in germ line cells, particularly in spermatogenesis. They are typically larger than miRNAs, ranging 26–31 nucleotides in size.
Pre-miRNA
pre-miRNAs have a characteristic stem-loop structure of about 70 nucleotides and are derived from primRNAs. They are the substrates for the DICER RNAse, which processes the pre-miRNA to produce short double-stranded RNA fragments.
Pri-miRNA
A microRNA molecule is synthesized as a long RNA primary transcript known as a pri-miRNA, which is cleaved by Drosha RNAse to produce a characteristic stem-loop structure of about 70 base pairs long, known as a pre-miRNA.
RNA-Induced Silencing Complex, (RISC)
The RISC complex acts in RNA interference and is a multiprotein complex that incorporates one strand of an siRNA or miRNA and uses this as a template for recognising a complementary mRNA target. When the complementary target strand is bound, the RISC RNase is activated, leading to cleavage of the target RNA. This process is important both in targeted gene regulation by microRNAs, but also as a defensive mechanism against viral infections, which often feature double-stranded RNA. The RISC complex is localized in the cell cytoplasm.
RNA intereference (RNAi)
RNA interference is a biological process in which small RNA molecules inhibit gene expression in a targeted manner. RNA interference can use two types of small RNA molecules to bring about this targeted inhibition of gene expression – microRNAs (miRNAs) and small interfering RNA (siRNAs). RNA interference has an important role in defending cells against parasitic nucleotide sequences (eg viruses), but also in directing development as well as gene expression in general.
Small hairpin RNA (shRNA)
Small hairpin RNAs (aka short hairpin RNAs) are experimentally used double stranded siRNA like molecules, where a tight hairpin turn is used to join the two complementary strands that constitute the siRNA moiety. This arrangement simplifies the construction of the siRNA, as only one RNA strand needs to be produced to make an siRNA like molecule through folding. shRNAs can be used to kock-down target gene expression through RNA interference (RNAi). As experimental tools, shRNAs are typically expressed in cells as recombinant molecules through plasmid, viral and bacterial vectors.
Small interfering RNA (siRNA)
siRNAs are a class of doublestranded RNA molecules, 20-25 base pairs in length. siRNAs act in RNA interference (RNAi), where they can interfere with gene expression specific through the use of nucleotide sequences that are complementary to the target mRNA.
