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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 ...
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.
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 ...
The microprocessor complex consists minimally of two proteins: Drosha, a ribonuclease III enzyme; and DGCR8, a double-stranded RNA binding protein. [4] [5] [6] (DGCR8 is the name used in mammalian genetics, abbreviated from "DiGeorge syndrome critical region 8"; the homologous protein in model organisms such as flies and worms is called Pasha, for Partner of Drosha.)
[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.
Also the degree of complementarity between the two strands of the intermediate RNA duplex defines how the miRNA are sorted into different types of Argonaute proteins. In animals, Argonaute associated with miRNA binds to the 3′-untranslated region of mRNA and prevents the production of proteins in various ways.
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.