Due to their widespread distribution and virulence, protozoan species of the genus Perkinsus are especially worrisome
parasites for shellfish farmers. In the present paper, we investigate the organization and the structural features of the
nuclear ribosomal genes of Perkinsus atlanticus as well as the use of DNA sequence information from this region for
phylogenetic analyses. This information has been useful, further, for the development of a diagnostic test based on the
amplification by the polymerase chain reaction (PCR) technique. We have isolated a high-copy DNA sequence in this
species, and, after its characterization, we have determined that it corresponds to the ribosomal RNA (rRNA) genes
28S–5S–18S and the intergenic spacers. By comparing the complete sequence of the 5S rRNA gene and a partial sequence
of the 18S rRNA gene of P. atlanticus with the sequences of those genes in other Alveolates, we have found additional
support for the hypothesis that Perkinsus is more closely related to species of Dinoflagellata than to species of Apicomplexa.
The intergenic spacer sequence between the 5S and the 18S rRNA genes was used to design a pair of primers to be used
as a PCR-based diagnostic test.The nucleotide sequence data reported in this paper are
available in the EMBL database with the accession number
AJ238400.The commercial use of the diagnostic test presented
here is protected by a patent. This patent is pending upon
the application number P9801511.