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miRNA biogenesis in plants differs from animal biogenesis mainly in the steps of nuclear processing and export. Instead of being cleaved by two different enzymes, once inside and once outside the nucleus, both cleavages of the plant miRNA are performed by a Dicer homolog, called Dicer-like1 (DL1). DL1 is expressed only in the nucleus of plant ...
Small RNA (sRNA) are polymeric RNA molecules that are less than 200 nucleotides in length, and are usually non-coding. [1] RNA silencing is often a function of these molecules, with the most common and well-studied example being RNA interference (RNAi), in which endogenously expressed microRNA (miRNA) or exogenously derived small interfering RNA (siRNA) induces the degradation of complementary ...
[1] [2] These short hairpin introns formed via atypical miRNA biogenesis pathways. [ 3 ] [ 4 ] Mirtrons arise from the spliced-out introns and are known to function in gene expression. Mirtrons were first identified in Drosophila melanogaster and Caenorhabditis elegans .
The RNase III Dicer is a critical member of RISC that initiates the RNA interference process by producing double-stranded siRNA or single-stranded miRNA. Enzymatic cleavage of dsRNA within the cell produces the short siRNA fragments of 21-23 nucleotides in length with a two-nucleotide 3' overhang.
It has been shown that human ACA45 is a bona fide snoRNA that can be processed into a 21-nucleotides-long mature miRNA by the RNAse III family endoribonuclease dicer. [34] This snoRNA product has previously been identified as mmu-miR-1839 and was shown to be processed independently from the other miRNA-generating endoribonuclease drosha. [35]
These two proteins homeostatically control miRNA biogenesis by an auto-feedback loop. [16] A 2nt 3' overhang is generated by Drosha in the nucleus recognized by Dicer in the cytoplasm, which couples the upstream and downstream processing events. Pre-miRNA is then further processed by the RNase Dicer into mature miRNAs in the cell cytoplasm.
Many mammalian genomes encode four closely related miR-29 precursors that are transcribed in two transcriptional units. For example, human miR-29a and miR-29b-1 are processed from an intron of a long non-coding transcript pri-miRNA (lnc-pri-miRNA) LOC646329 from chromosome 7. miR-29b-2 (identical in sequence to miR-29b-1) and miR-29c are co-transcribed from chromosome 1.
Although DCL1, also called Endoribonuclease Dicer homolog 1, is named for its homology with the metazoan protein Dicer, its role in miRNA biogenesis is somewhat different, due to substantial differences in miRNA maturation processes between plants and animals, [2] as well due to additional downstream plant-specific pathways, where DCL1 paralogs ...