EVIDENCE FOR A SINGLE ORIGIN OF THE 35 KB PLASTID DNA IN APICOMPLEXANS

Gene organization on three selected parts of the 35-kb plastid DNA of the malaria parasite Plasmodium falciparum was compared with that of t wo other apicomplexans, namely Toxoplasma gondii and Eimeria tenella, This comparison included the characteristic inverted ribosomal RNA rep eat, A short segment of DNA from Theileria annulata also was included in a separate comparison, Criteria such as the presence or absence of particular genes, their map positions and their sequences, were used t o assess whether the apicomplexan plastid DNAs originated from a singl e origin (a unitary hypothesis for the entire phylum), or whether disp arate multiple events were more likely, The results provisionally favo ur a single origin although clearly this comparison of the apicomplexa n plDNAs is still fragmentary, Contrary to the tendency towards homoge neity, evidence was found that the coccidian plastids may have evolved a suppressor mechanism for UGA stop codons.