RNA is a versatile molecule with a central role in many biological processes. RNAs are rarely found in isolation in the cells. Rather, they associate with RNA-binding proteins (RBPs) to form ribonucleoproteins (RNPs). Typically, RBPs are characterized by a modular domain organization, and most of them consist of only a few basic RNA-binding domains (RBDs) repeated in tandem. To carry out their multiplicity of functions, RBDs use a range of binding modes to interact with a variety of RNA structures. In the present thesis, functional and structural studies of two RBDs, was carried out: the double-strand RNA binding Domain (dsRBD) of the Adenosine Deaminase Acting on RNA (ADAR) enzymes, and the RNA Recognition Motifs (RRMs) contained in the SMRT/HDAC1 Associated Repressor Protein (SHARP). This study provides new insights into RNA-protein interactions, and it contributes and enriches the already extended repertoire of the RBDs recognition modes.