[MiRNA--new mechanisms of gene expression control].

MicroRNAs are small, non-coding RNAs that regulate gene expression on post-transcriptional level. When included in RISC complex they bind to 3' UTR of target gene implicating inhibition of translation or mRNA degradation. Primary miRNA transcripts are several hundred nucleotides long, during maturation they have typical hairpin secondary structure. Active, mature miRNA is a single-stranded molecule 21-23 nt long. Human miRNA genes may constitute even 2% of the genome. miRNA molecules influence the expression of over 30% of structural genes. Paper presents current knowledge about miRNA biogenesis, types of small non-coding RNAs that are biologically functional, mechanisms of gene expression regulation they exert and the role of miRNA in oncogenesis.