Expression plasmids were constructed with genes encoding the ILOX3, ILOX6, and ILOX9 recombinant proteins, which contain the C-terminal fragments of trimer, hexamer, or nonamer of oxytocinoyl-Lys. Upon expression in E. coli, all three genes yielded inclusion bodies containing protein products of similar length and heterogeneous in the C-terminal region. It is likely that in the case of the ilox3 gene, the obtained protein mixture includes the full-length product of translation with the C-terminal lysine. In the case of the ilox6 and ilox9 genes, the protein products are formed as the result of a site-specific proteolysis in the regions between the second and the fourth oxytocin units.