The cloned rRNA genes of P. lophurae: a novel rDNA structure

The detailed structure of two ribosomal DNA (rDNA) clones CL-1 and HA-2, from the avian malaria parasite Plasmodium lophurae has been examined using hybridization and electron microscopy. The results demonstrate that the clone CL-1 contains two regions homologous to 25s rRNA of approximately 2200 base pairs (bp) and 450 bp in length, separated by a non homologous region of 240 bp. CL-1 also contains two regions of approximately 1100 bp and 550 bp homologous to 17s rRNA, separated by a non homologous region of 230 bp. The clone HA-2 contains a single region of 670 bp, which is homologous to 25s rRNA. This region is flanked by non homologous stretches of DNA 940 bp and 110 bp in length. As HA-2 is known to be adjacent to CL-1 in the genome (1), these results suggest that the 25s rDNA is interrupted twice, and the 17s rDNA once, by stretches of DNA not found in mature rRNA.