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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]
[2] There are four main variation types: 5' trimming—the 5' dicing site is upstream or downstream from the reference miRNA sequence; 3' trimming—the 3' dicing site is upstream or downstream from the reference miRNA sequence; 3' nucleotide addition—nucleotides added to the 3' end of the reference miRNA
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.
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 ...
Each member of miR-125 family has two different variants of mature miRNAs - 5p and 3p. Both variants originate from the same pre-miRNA. MiR-125-5p variant generally shows higher expression compared to miR-125-3p. [6] In humans, miR-125 family is composed of three homologs: hsa-miR-125a, hsa-miR-125b-1 and hsa-miR-125b-2. [7]
The lethal-7 (let-7) gene was first discovered in the nematode C. elegans as a key developmental regulator and became one of the first two known microRNAs (the other one is lin-4). [8] Soon, let-7 was found in the fruit fly (Drosophila), and identified as the first known human miRNA by a BLAST (basic local alignment search tool) research. [9]
[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 . [ 5 ] [ 6 ] The number of mirtrons identified to date are 14, 9, and 19 in D. melanogaster, C. elegans and mammals respectively. [ 7 ]
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.