miRNAs are short non-protein coding RNAs, being though a crucial regulators of gene expression of up to 90%
of human genes (Friedmann et al., 2009; Guo et al., 2010; Perron and Provost, 2010; Bartel, 2009; Esquela-Kerscher
and Slack, 2006; Bartel, 2006; Kozomara and Griffiths-Jones, 2011; Selbach et al., 2008). These tiny RNA
molecules tune cell growth, tissue differentiation, cell proliferation, embryonic development, apoptosis and cellular
signaling (Gaur et al., 2007; Godlewski et al., 2012; Kim et al., 2010; Cui et al., 2006). Even slight shift in
miRNA level could lead to significant changes of transcriptome, and in a result of cell phenotype. In the last decade,
over 30 000 mature miRNA sequences were deposited in miRBase (Griffiths-Jones et al., 2006). The function
of many of them have been found and anti-miRNA tools, as potential therapy approach have been designed.
Despite of an enormous data of miRNA, there are still many questions concerning miRNA function to be solved.
Following Francis Crick’s famous statement “If you want to understand function, study structure”, we were
looking for structure of mature miRNAs (Belter et al., 2014).