introduction of three independent selection markers in leishmania

the ple2scx vector was developed for the stable expression of exogenous genes in the protozoan parasite leishmania. the ple2scx construct contains three independent selection markers: herpes simplex virus thymidine kinase (hsv-tk), cytosine deaminase (cd) and streptothericin acetyltransferase gene (sat) in multiple cloning site, flanking by 5’ and 3’ untranslated regions of the previously cloned leishmania major hexa-binding protein gene. selection was based on resistance to the nourseothericin (ns) which corresponds to sat gene. the two negative selection hsv-tk and cd genes, make the transformed cell sensitive to ganciclovir (gcv) and 5-fluorocytosine (5-fc). the vector was introduced into leishmania promastigotes by electroporation and maintained as circular form. the selected transfectants were not grown on media with gcv or 5-fc. using two drug sensitive selectable markers together on a vector is a novel strategy in gene cloning in leishmania. this stable transfection vector has allowed the permanently expression of several different exogenous genes at the same time in leishmania