tructures called ‘spindle pole bodies’ resemble those of yeast. Chitin, a major polysaccharide of the fungal cell wall, is present in the inner part of the microsporidian spore wall. Trehalose, a disaccharide Sodium laureth sulfate price frequently found in fungi, has also been detected in microsporidia. The parasite’s infections have medical importance since its hosts include various mammals, including humans, where it is known to cause digestive and clinical syndromes affecting the nervous system in HIV-infected or cyclosporine-treated patients. The small and compact 2.9 Mb genome of E. cuniculi has recently been sequenced and characterised. It split into 11 linear chromosomes harbouring 1,997 proteincoding sequences in a tightly clustered configuration. This degree of compaction has been achieved partly by reducing rDNA sequences as well as many protein-coding genes and intergenic regions. E. cuniculi is therefore a microbial eukaryote that is highly-adapted to its parasitic lifestyle, and its genome sequence provides an opportunity for cataloguing the proteins that constitute its signal transduction networks. This understanding should shed light into the molecular mechanisms of pathogenicity and, from a wider perspective, on the minimal protein kinasebased signal transduction requirements of a eukaryotic intracellular parasite. Reversible protein phosphorylation plays a central role in most cellular processes. Deregulation of protein phosphorylation is at the origin of several pathologies and protein kinases are now considered promising drug targets ]. Indeed, the first kinase inhibitors to be developed as drugs have recently been made available on the market. The currently accepted classification of protein kinases splits the protein PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19792551 kinase superfamily into ‘conventional’ protein kinases and ‘atypical’ protein kinases. ePKs are the largest group and have been sub-classified into 8 families by examining sequence similarity between catalytic domains, the presence of accessory domains, and by considering modes of regulation. The 8 ePK families are: the AGC family; the CAMKs; the CK1 family; the CMGC family; the RGC family; the STE family; the TK family; and the TKL family. A ninth group, called the ‘Other’ group, consists of a mixed collection of kinases that could not be classified easily into the previous ePK families. The aPKs are a small set of protein kinases that do not share clear sequence similarity with ePKs but have been shown experimentally to have protein kinase activity, and comprise the following bona fide families: Alpha; PIKK; PDHK; and RIO. Protein kinases controlling the proliferation and development of parasitic eukaryotes represent attractive drug tarPage 2 of 21 BMC Genomics 2007, 8:309 http://www.biomedcentral.com/1471-2164/8/309 gets, because they are likely to be essential to parasite multiplication and/or development; and these enzymes 
display structural and functional divergence when compared to their mammalian counterparts, suggesting that specific inhibition can be achieved. Furthermore, the importance of protein kinases in most crucial cellular processes makes them interesting subjects of fundamental investigations into the cell biology of parasitic eukaryotes. The availability of the entire genome sequences of several parasites permits the study of their protein kinase complements. Hence, two recent studies reported the characterisation of the kinomes of the malaria parasite Plasmodiumfalciparum, showing that this organism possesses
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