LOCALIZATION OF RIBOSOMAL-RNA AND PBS21-MESSENGER-RNA IN THE SEXUAL STAGES OF PLASMODIUM-BERGHEI USING ELECTRON-MICROSCOPE IN-SITU HYBRIDIZATION

A reproducible technique for the ultrastructural localization of RNAs in malaria parasites has been developed which combines excellent struc tural preservation with high hybridization signals, Signals obtained f ollowing in situ hybridization with an antisense rRNA probe which reco gnizes all forms of small subunit (SSU) rRNA correlate with the densit y of ribosomes in the parasite cytoplasm and show that a) the male gam etocyte has only 12 to 25% the ribosomes found in the female cell and asexual parasite and b) the probe did not hybridize with an electron-d ense nuclear body previously called a nucleolus, We suggest this struc ture is either a transcription-, or a replication-factory Using a prob e for the sexual stage-specific protein Pbs21 mRNA, signal was found o nly in female gametocytes, zygotes and ookinetes and showed a non-rand om, clumped cytoplasmic distribution. It is not known at present wheth er the non-random distribution of the Pbs21 mRNA is critical to the ve ry delayed translation of the Pbs21 message into protein, which occurs only in the zygote and ookinete.