Triple-transfectants were generated by transfection of Leishmania major pX-alad and p6.5-pbgd double-transfectants with pXG-urod (see Materials and Methods). [A] Triple-and double-transfectants grown under the full strengths of their respective selective pressures, i. e. 20 ug/ml tunicamycin+100 ug/ml G418+500 ug/ml hygromycin and 20 ug/ml tunicamycin+100 ug/ml G418, respectively; [B] As [A], except the triple-transfectants were grown for 4 passages in 1 month under the single selective pressure of hygromycin at 1 mg/ml for urod. All samples were incubated in the presence and absence of 1 mM ALA (± ALA) for 48 hrs in the dark and processed for porphyrin analyses by TLC as described. Stars and pound sign, Incompletely decarboxylated intermediates in addition to URO and COPRO produced by the triple-transfectants in [A]. URO and COPRO are the only two species produced by the triple-transfectants in [B]. See legend to Fig. 3C for porphyrin markers, and to Fig. 3A and text for ±alad, pbdg and urod.