Vol. 11, Issue 2, 198-207, February 2001

REPORTS
Sequence and Analysis of Chromosome I of the Amitochondriate Intracellular Parasite Encephalitozoon cuniculi (Microspora)

¹ Equipe de Parasitologie Moléculaire et Cellulaire, LBP, UMR CNRS 6023, Université Blaise Pascal, 63177 Aubière Cedex, France; ² UMR CNRS 8030, CP 5706, 91057 Evry Cedex, France; ³ Genoscope, CP 5706, 91057 Evry Cedex, France

A DNA sequencing program was applied to the small (<3 Mb) genome of the microsporidian Encephalitozoon cuniculi, an amitochondriate eukaryotic parasite of mammals, and the sequence of the smallest chromosome was determined. The ~224-kb E. cuniculi chromosome I exhibits a dyad symmetry characterized by two identical 37-kb subtelomeric regions which are divergently oriented and extend just downstream of the inverted copies of an 8-kb duplicated cluster of six genes. Each subtelomeric region comprises a single 16S-23S rDNA transcription unit, flanked by various tandemly repeated sequences, and ends with ~1 kb of heterogeneous telomeric repeats. The central (or core) region of the chromosome harbors a highly compact arrangement of 132 potential protein-coding genes plus two tRNA genes (one gene per 1.14 kb). Most genes occur as single copies with no identified introns. Of these putative genes, only 53 could be assigned to known functions. A number of genes from the transcription and translation machineries as well as from other cellular processes display characteristic eukaryotic signatures or are clearly eukaryote-specific.

[The sequence data described in this paper have been submitted to the EMBL data library under accession no. AL 391737.]