TRANSITION OF PLASMODIUM-VIVAX RIBOSOME TYPES CORRESPONDS TO SPOROZOITE DIFFERENTIATION IN THE MOSQUITO

Two distinct small subunit ribosomal RNA (SSUrRNA) genes were amplifie d from the genomic DNA of Plasmodium vivax. Comparison of the two codi ng sequences reveals an overall divergence of 14.5% and most differenc es are clustered into the regions known to diverge rapidly in all euka ryotic SSUrRNAs. Oligonucleotides complementary to unique sequences of each gene have been used to distinguish the transcripts expressed eit her at schizogony in human blood (A gene) or at sporogony in the mosqu ito (C gene). These oligonucleotides were also used to monitor turnove r of ribosomes during parasite development in mosquitoes. Transcripts of the A gene were predominant in the infected human blood and engorge d mosquitoes but disappeared within 24 h after feeding. Expression of the C gene in mosquitoes was not detected until day 6 after the blood meal. A period of rapid accumulation of the C type rRNA from day 6 to day 8 corresponds to differentiation of individual sporozoites within the oocyst. Possible functional implications relating to the timing of this transition are discussed.