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miR-92 is part of a large precursor sequence that forms a stem loop once transcribed into RNA. This long precursor sequence is a component of the mir-17-92 cluster which contains 5 additional mir precursor sequences: mir-17, mir-18a, mir-19a, mir-20a and mir19b-1. [4]
In the past it had always been said that the same miRNA precursor generates the same miRNA sequences. However, the advent of deep sequencing has now allowed researchers to detect a huge variability in miRNA biogenesis, meaning that from the same miRNA precursor many different sequences can be generated potentially have different targets, [ 3 ...
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 ...
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.
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.
AGO2 (grey) in complex with a microRNA (light blue) and its target mRNA (dark blue) In humans, there are eight AGO family members, some of which are investigated intensively. However, even though AGO1–4 are capable of loading miRNA, endonuclease activity and thus RNAi-dependent gene silencing exclusively belongs to AGO2.
The Let-7 microRNA precursor gives rise to let-7, a microRNA (miRNA) involved in control of stem-cell division and differentiation. [ 1 ] let-7 , short for "lethal-7", was discovered along with the miRNA lin-4 in a study of developmental timing in C. elegans , [ 2 ] making these miRNAs the first ever discovered.
A miRNA can be derived from each arm of the pre-miRNA hairpin. Historically, the least common of these two miRNA products was denoted by the addition of * to the miRNA name, however the modern convention is to denote mature miRNA products as 5p or 3p. [11] Both mir-10 and mir-10* have been detected in Drosophila.