CHIMERIC RIBOSOMAL-RNAS CONTAINING THE GTPASE CENTERS OF THE DEVELOPMENTALLY-REGULATED RIBOSOMAL RIBOSOMAL-RNAS OF PLASMODIUM-FALCIPARUM ARE FUNCTIONALLY DISTINCT

The human malaria parasite, Plasmodium falciparum, maintains at least two distinct types, A and S, of developmentally controlled ribosomal R NAs. To investigate specific functions associated with these rRNAs, we replaced the Saccharomyces cerevisiae GTPase domain of the 25S rRNA w ith GTPase domains corresponding to the Plasmodium A-and S-type 28S rR NAs, The A-type rRNA differs in a single nonconserved base pair from t he yeast GTPase domain, The S-type rRNA GTPase domain has three additi onal changes in highly conserved residues, making it unique among all known rRNA sequences. The expression of either A-or S-type chimeric rR NA in yeast increased translational accuracy, Yeast containing only A- type chimeric rRNA and no wild-type yeast rRNA grew at the wild-type l evel. In contrast, S-type chimeric rRNA severely inhibited growth in t he presence of wild-type yeast rRNA, and caused lethality in the absen ce of the wild-type yeast rRNA, We show what before could only be hypo thesized, that the changes in the GTPase center of ribosomes present d uring different developmental stages of Plasmodium species can result in fundamental changes in the biology of the organism.