Recent annotated sequencing data found that 22 different organisms including, mammals, amphibians, birds, reptiles, sea squirts, and sea lampreys, express a conserved miR-155-5p. Evolutionary conservation Įarly phylogenetic analyses demonstrated that the sequence of pre-mir-155 and miR-155-5p was conserved between human, mouse, and chicken. inhibition of translation initiation) and/or degradation following deadenylation. Finally, with the miR-155-5p/-3p acting as an adaptor for the RISC, complex-bound mRNAs are subjected to translational repression (i.e. Once miR-155-5p/-3p is assembled into the RISC, these molecules subsequently recognize their target messenger RNA ( mRNA) by base pairing interactions between nucleotides 2 and 8 of miR-155-5p/-3p (the seed region) and complementary nucleotides predominantly in the 3′-untranslated region ( 3′-UTR) of mRNAs (see Figure 4 and 5 below). The mature miR-155 (miR-155-5p) sequence is shown in green and mature miR-155* (miR-155-3p) sequence is shown in red. miR-155-3p) following their name (see Figure 3). Due to the increasing number of examples where two functional mature miRNAs are processed from opposite arms of the same pre-miRNA, pre-mir-155 products are now denoted with the suffix -5p (from the 5′ arm) (e.g. Recent data suggest that both arms of the pre-miRNA hairpin can give rise to mature miRNAs. In a manner similar to siRNA duplexes, one of the two strands, the "passenger miRNA" (miR-155*), is released and degraded while the other strand, designated the "guide strand" or "mature miRNA" (miR-155), is retained within the RISC. Following Dicer cleavage, an Argonaute (Ago) protein binds to the short RNA duplexes, forming the core of a multi-subunit complex called the RNA-induced silencing complex ( RISC). The mature miR-155 (miR-155-5p) sequence is shown in green and mature miR-155* (miR-155-3p) sequence is shown in red.įollowing export from the nucleus by exportin-5, pre-mir-155 molecules are cleaved near the terminal loop by Dicer resulting in RNA duplexes of ~22nucleotides. The sequence of the pre-mir-155 stem loop that is matured from the pri-miRNA transcript. Once miR-155 pri-miRNA is transcribed, this transcript is cleaved by the nuclear microprocessor complex, of which the core components are the RNase III type endonuclease Drosha and the DiGeorge critical region 8 ( DGCR8) protein, to produce a 65 nucleotide stem-loop precursor miRNA (pre-mir-155) (see Figure 2).įigure 2. This non-coding RNA ( ncRNA) is now defined as a primary-miRNA (pri-miRNA). The MIR155HG RNA transcript does not contain a long open reading frame (ORF), however, it does include an imperfectly base-paired stem loop that is conserved across species. ![]() The location of the pre-mir-155 is denoted by the orange box. ![]() This gene spans 13024 bp, is composed of three exons, and encodes a 1500 bp non-coding primary-miRNA (pri-miRNA) (accession # NR_001458). Schematic representation of the MIR155HG (accession # NC_000021). The 23 nucleotide single-stranded miR-155, which is harbored in exon 3, is subsequently processed from the parent RNA molecule. The MIR155HG is transcribed by RNA polymerase II and the resulting ~1,500 nucleotide RNA is capped and polyadenylated. The MIR155HG was initially identified as a gene that was transcriptionally activated by promoter insertion at a common retroviral integration site in B-cell lymphomas and was formerly called BIC (B-cell Integration Cluster). Exogenous molecular control in vivo of miR-155 expression may inhibit malignant growth, viral infections, and enhance the progression of cardiovascular diseases. MiR-155 plays a role in various physiological and pathological processes. ![]() MiR-155 is a microRNA that in humans is encoded by the MIR155 host gene or MIR155HG.
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