MicroARN

The Micro ARN (miRNA) are long ARN simple-bit from approximately 21 to 24 nucleotides. There exist several hundreds of Gène S of microARN in the genomes of the majority of the pluricellular organizations. The miRNA are répresseurs post-transcriptionnels: while being paired with ARN messengers, they guide their degradation, or the repression of their translation in Protéine.

The genes of miRNA are transcribed in the shape of long precursors (called “pri-miRNA”); these precursors are cleaved (at the Animaux, this reaction is catalyzed by the Drosha enzyme; at the Plants, by an enzyme of the Dicer family) in an intermediate product, called “pre-miRNA”. The preone is a long ARN of approximately 70 nucleotides, folded up in stem-buckles imperfect by complementarity of bases between first half and second half of its sequence. The preone is then cleaved by an enzyme of the Dicer family which releases it from the loop (in the Animals, this reaction proceeds in the Cytoplasme; it is nuclear at the Plants), to release a small ARN double-bit: in this small duplex (long of a score of pairs of bases, with approximately 2 nucleotides simple bit at end 3 ' of each bit), the future miRNA imperfectly is paired with a similar molecule (small long ARN of a score of nucleotides), called “miRNA*”.

During the last stage of the maturation of the miRNA, this duplex is open; the miRNA joins a protein of the Argonaute family forming the complex " thus; RISC" , whereas the miRNA* is degraded.

The Dicer enzymes are also responsible for the production for interfering small ARN (or siRNA) starting from long ARN double-bit, during the process of interference with ARN. This process was described at the plant like being able to be an antiviral defense.

References

This publication (in English) definite the miRNAs and proposes ways to be followed to classify like miRNAs, of the genes coding ARN. Victor Ambros, Bonnie Bartel, David P. Bartel, Christopher B. Burge, James C. Carrington, Xuemei Chen, Gideon Dreyfuss, Sean R. Eddy, Sam Griffiths-Jones, Mhairi Marshall, Marjori Matzke, Gary Ruvkun and Thomas Tuschl (2003) " With uniform system for microRNA annotation" , RNA , 9:277 - 279.
This publication (in English) discusses the processes where the siRNAs and the miRNA are implied, in the context of two articles published in the newspaper Science . David Baulcombe (2002) " Year RNA Microcosm" , Science , 297:2002 - 2003.
This publication (in English) described the discovery of " flax-4" , the first miRNA discovered at C.elegans. Lee, R.C., Feinbaum, R.L and Ambros, V. (1993) " The C. elegans heterochronic embarrassment flax-4 encodes small RNAs with antisense complementarity to flax-14 " , Concealment , 75:843 - 854.

External bond

a small animation explaining how can act these ARN.
The miRNA Registry

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