en Introduction of Three Independent Selection Markers in Leishmania مقاله کامل Full Length/Original Article <font face="times new roman,times,serif">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&rsquo; and 3&rsquo; 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 </font> HSV-thymidine kinase (HSV-TK), Cytosine deaminase (CD), ganciclovir (GCV), 5-fluorocytosine (5-FC), nourseothericin (Ns) 13 18 http://ibj.pasteur.ac.ir/browse.php?a_code=A-10-1-281&slc_lang=en&sid=1 Noushin Davoudi نوشین داوودی No Fereidoun Mahboudi فریدون مهبودی Yes Mohammad Azizi محمد عزیزی No Ahmad Adeli احمد عادلی No Robert. W McMaster Robert. W McMaster No