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MicroRNA

MicroRNA. INTRODUCTION. miRNAs are RNA genes which are transcribed from DNA, but are not translated into protein . A miRNA (micro-RNA) is a form of single-stranded RNA which is typically 20-25 nucleotide long . It is thought to regulate the expression of other genes.

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MicroRNA

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  1. MicroRNA

  2. INTRODUCTION • miRNAs are RNA genes which are transcribedfrom DNA, but are nottranslatedintoprotein. • A miRNA (micro-RNA) is a form of single-stranded RNA which is typically 20-25 nucleotide long. • It is thought to regulate the expression of other genes. • The DNA sequencethatcodesforanmiRNA gene islongerthanthemiRNAitself. This DNA sequenceincludesthemiRNAsequence and anapproximate reverse complement

  3. FORMATION OF miRNA • When this DNA sequence istranscribed into a single-stranded RNA molecule, the miRNA sequence and its reverse-complement base pair to form a double stranded RNA hairpin loop; this forms a primary miRNA structure (pri-miRNA)

  4. In animals: the nuclear enzyme Drosha cleaves the base of the hairpin to form pre-miRNA. The pre-miRNA molecule is then actively transported out of the nucleus into the cytoplasm by Exportin 5, a carrier protein. The Dicer enzyme then cuts 20-25 nucleotides from the base of the hairpin to release the mature miRNA. • In plants: which lack Drosha homologues, pri- and pre-miRNA processing by Dicer probably takesplace in the nucleus, and mature miRNA duplexes are exported to the cytosol by Exportin 5.

  5. FUNCTION OF miRNA • Mature miRNA molecules are either fully or partially complementary to one or more messenger RNA (mRNA) molecules, and their main function is to down-regulate gene expression. • Animal miRNAs are usually complementary to a site in the 3' UTR • whereas plant miRNAs are usually complementary to coding regions of mRNAs. Perfect or near perfect base pairing with the target RNA promotes cleavage of the RNA • miRNAs function in association with a complement of proteins collectively termed the miRNP

  6. DETECTION OF miRNA • MicroRNA expression can be quantified by being profiled against a database describing thousands of known miRNAs using microarray technology • It was initially thought that miRNA genes were located in intergenic regions, however, later study showed that several miRNA genes were located within introns of either protein-coding or noncodinggenes while only a few were located in exons of noncoding RNAs or UTR of protein coding genes

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