[en] The aim of this PhD thesis is to contribute to the biochemical and structural characterization of the Na/I sym-porter (NIS) for which the knowledge of the molecular bases of the ionic selectivity and of the active transport is very fragmentary. In a first part has been studied the soluble c-terminal part of the protein (90 amino acids). This protein part has been expressed separately, with a thioredoxin in a bacterial system (Escherichia Coli). It has then been purified to allow its structural characterization. The analyses by circular dichroism and NMR have nevertheless reveal that this fragment has no three-dimensional structure. The second part of this study has allowed to reveal the systematic co-purification with an entire protein of a c-terminal fragment having a transmembrane part. The study of this fragment will allow to explain its existence and potential role in the NIS regulation. (O.M.)