The present invention refers to uses of crotamine and compositions containing it, based on its characteristic of interaction with genetic material. Under submicromolar quantities, the polypeptide is no longer toxic, presenting the characteristics properties of cell penetration, transport of molecules to the surface, cytoplasm or cell nucleus and particularly, selective cell penetration.The invention also refers to compositions comprising a pharmaceutically effective concentration of crotamine and its use for the treatment of diseases and dysfunctions, based on its characteristics of interaction with genetic material, such as DNA and RNA, and cell selectivity.Further, the invention refers to a kit comprising crotamine as a reagent to: (i) transfect or carry molecules to the surface, cytoplasm or nucleus of the cell or (ii) identify and select actively proliferating cells in a homogeneous and/or mixed cell population, particularly the ones originated from the umbilical cord and/or bone marrow and others undifferentiated cells such as progenitors and stem cells from different sources of organism and cancer cells.