THE SECRETORY PATHWAY OF PLASMODIUM-FALCIPARUM REGULATES TRANSPORT OFP82 RAP-1 TO THE RHOPTRIES/

The rhoptries of Plasmodium falciparum are formed during a restricted period in the asexual erythrocytic cycle. The steps required for rhopt ry biogenesis and the pathway for targeting proteins to the rhoptries have not been elucidated. Using the maturation of the Rhoptry-Associat ed Protein 1 (RAP-1) gene product to study these steps, it is reported here that a secretory pathway controls transport of protein complexes containing RAP-1 products to the rhoptries. Both brefeldin A (BFA) an d low temperature reversibly block the processing of an 86-kDa precurs or (Pr86) to the mature 82-kDa RAP-1 product (p82). Furthermore, the p oints of action of BFA and low temperature appear to overlap since the ir sequential application reversibly prevents Pr86 processing. Treatme nt of intact cells with N-ethylmaleimide, which prevents the fusion of transport vesicles with Golgi membranes in other eukaryotic cells, ir reversibly blocks processing of Pr86. The role of the secretory pathwa y in targeting p82 protein complexes to the rhoptries is further suppo rted by the observed co-translational translocation into canine micros omes of the in vitro translation product of RAP-1. These in vitro resu lts also reveal that the RAP-1 product contains a cleavable N-terminal signal peptide and appears to be initially synthesized as an 84-kDa p rotein. The above data indicate that transport of p82 to the rhoptries is regulated by the secretory pathway and that the RAP-1 primary tran slation product differs in apparent molecular weight from the in vivo precursor Pr86. Our results suggest that rhoptry biogenesis is control led in part by the secretory pathway and that the RAP-1 gene product a cquires a previously undetected protein modification during its matura tion.