ELSEVfER Molecular and Biochemical Parasitology 74 (1995) 229-231 zyxwvutsrqponmlkjihgfedcbaZYX MOLECULAR ii!&EMKAL PARASITOLOGY Short communication Evidence for the smallest nuclear genome (2.9 Mb) in the microsporidium zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Encephalitozoon cuniculi Corinne Biderrea, Michel Pagkb, Guy MktCnier”, Elizabeth U. Canning’, Christian P. Viva&* a zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO “Laboratoire de Proiistologie mokulaire et celhdaire des parasites, URA CNRS 1944. UniversirP Blaise Pascal. Biologie A, 63177 Aubke Cedex. France bLaboratoire GPnome des Parasites. UniversitP Montpellier I. Rue Augusre-Broussonnet, 34000 Montpellier. France ‘Department of Biology, Imperial College of Science, Technology, and Medicine. London 5 W7 ZAZ. England, UK Received 27 June 1995; revision received 7 September 1995; accepted 7 September 1995 zyxwvutsrqponmlkjihgf Keywoxk PFGE; Molecular karyotype; Protozoa; Microsporidia; Encephalirozoon cuniculi Among unicellular eukaryotes, microsporidia are obligately intracellular amitochondrial para- sites and are considered to be of very ancient ori- gin as deduced from the prokaryotic features of their ribosomes [1,2] and rRNA phylogenies [3]. On the assumption that they are primitively amitochondrial, they have been included, with Metamonada and Archamoebae, in a new kingdom, the Archezoa. Conceivably, archezoan cells originated from a single prokaryotic ancestor 141. Pulsed-field gel electrophoresis (PFGE) studies on the karyotypes of several species have shown that the haploid genome size ranges from only 5.3 to 19.5 Mb (5-91, indicating that C-value paradox also exists for Microsporidia. The present work concerns the karyotyping of Encephalitozoon *Corresponding author, Tel.: t33 73407457: Fax: +33 73407670; E-mail: vivares@cisun.univ-bpclermont.fr. cuniculi which has been incriminated as an oppor- tunistic parasite in AIDS patients [lo]. DNA sepa- ration was performed by contour-clamped homogeneous electric field (CHEF) electro- phoresis. To get some information on ploidy of microsporidian nuclei, the total DNA content of spores was determined by a diphenylamine colori- metric procedure [ 111. Electrophoretic karyotypes of E. cuniculi are shown in Fig. 1. Eleven chromosomal DNA bands were finally resolved, the estimated molecular sizes being: I, 217 kb; II, 235 kb; III, 241 kb; IV, 247 kb; V, 251 kb; VI, 257 kb; VII, 266 kb; VIII, 272 kb; IX, 290 kb; X, 304 kb; XI, 315 kb. It should be noted that experiments of longer duration pulses did not provide evidence for unresolved DNA molecules beyond 2 Mb. The same banding pat- tern was observed when using samples of parasitiz- ed host cells, the higher molecuIar weight DNA of the host cells being unresolved within a compres- 0166-6851/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0166-6851(95)02495-Y