MicroRNAs are essential gene regulators in multicellular organisms. Plant miRNA precursors (pri-miRNAs) are processed in the nucleus by a protein complex formed by DICER-LIKE1 (DCL1), HYL1 and SERRATE. DCL1 performs two sequential cleavage steps on the precursor in order to excise the functional miRNA. It has been shown that the double stranded RNA binding domains of DCL1 and HYL1 are essential to ensure the accuracy of the processing reaction. The mechanism by which these domains position DCL1 at the correct location within the precursor is unknown. Pri-miRNAs display highly variable secondary structure features that could be essential to define the location of the miRNAs within their sequences. In this project we propose to characterize experimentally the secondary structure of different precursors and map the binding sites of the different proteins involved in the processing reaction, with the final goal of generating a model that allows us to explain the recognition of the precise cleavage site for the miRNA excision.