Biogenesis and mechanisms of microRNA‐mediated gene regulation

Abstract Endogenous RNAs that control posttranscriptional gene expression are microRNAs (miRNAs). These small regulatory molecules play a crucial role in certain biological processes and their expression is often strictly regulated. They are small 21–24 nucleotide molecules that act as major regulators of gene expression at the posttranscriptional level. One of the mechanisms by which miRNAs control the gene expression is to interact the interaction of the seeds with the 3ʹ‐end and and more seldom the 5ʹ‐end of mRNA transcribed by the target genes. miRNAs have been identified as important cytoplasmic regulators of gene expression. miRNAs function as posttranscriptional regulators of their messenger RNA (mRNA) targets by mRNA degradation and/or translational repression. It is becoming evident, however, that miRNAs have nuclear functions as well. About the cell type, the physiological state of the body, and various external factors, the following explanation will summarize the complex multilevel regulation of miRNA expression. A better understanding of the molecular mechanisms controlling miRNA expression will provide clarification of the variations in the expression of protein‐coding genes.