COMPARISON OF THE LARGE SUBUNIT RIBOSOMAL DNA OF NEOSPORA AND TOXOPLASMA AND DEVELOPMENT OF A NEW GENETIC-MARKER FOR THEIR DIFFERENTIATION BASED ON THE D2 DOMAIN

The latest release of the large subunit ribosomal database contains 42 9 sequences, yet only 10 (six nuclear and four mitochondrial) are deri ved from parasites of the phylum Apicomplexa. Three of these (all Toxo plasma gondii) were previously contained in the 1994 release of the da tabase. As an initiative towards an understanding of ribosomal gene or ganization in the Apicomplexa, the primary sequence of the large subun it (LSU) rDNA of Neospora caninum is presented, and compared with a co nsensus sequence derived for the LSU rDNA of T. gondii. Nucleotide dif ferences observed between these two taxa in the D2 expansion segment ( or domain) (also called the C1/C1' region) of the LSU rDNA were incorp orated into a primer that forms the basis of a species-specific polyme rase chain reaction (PCR) for N. caninum. The D2 domain of the LSU rDN A, therefore, represents a new genetic marker that can be used for the differentiation and identification of Neospora from other cyst-formin g coccidia. (C) 1998 Academic Press Limited.