Micro-RNAs (miRNAs): genomic organisation, biogenesis and mode of action.

MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression in animals and in plants. In recent years, miRNAs have been shown to be important biological molecules for regulating various cellular functions. miRNAs function post-transcriptionally usually by base-pairing to the mRNA 3'-untranslated regions of the mRNAs and repress protein synthesis by mechanisms that are not fully understood. Various miRNA genes have been mapped in the genome of a number of organisms and the list continues to grow. Details regarding the genomic organisation, transcriptional regulation and post-transcriptional maturation of miRNAs are still emerging. In this review, information regarding the genomic organisation, biogenesis and regulation of expression of miRNAs is discussed.