The primary structure of the rRNA insertions of Plasmodium lophurae

The DNA sequences of the novel insertion in the 17s rRNA gene and the large insertion in the 25s rRNA gene in the cloned rDNA unit of the avian malaria parasite Plasmodium lophurae are presented, together with a partial sequence of the flanking regions, which code for the mature rRNA. The homology of the mature rRNA coding regions with the rRNA sequences of other eukaryotic organisms is extensive, indicating that the plasmodium rRNA is structurally similar to other eukaryotes. Sequence data also reveal that the region 3' to the insertion in the 17s rRNA contains a second small inserted DNA sequence, in contrast to other known small rRNA sequences. The region containing the 25s insertion shares sequence homology and some secondary structure characteristics with the terminal direct repeat of the Drosophila melanogaster transposable element copia. This is the first such sequence described in plasmodia. The direction of transcription of the cloned rDNA unit of P. lophurae has also been determined. As in other organisms, the direction of transcription is found to be 5' 17s-25s 3'.