It is proposed that after cleavage of a PEST sequence, the exposed termini serve as unstructured initiation site for ubiquitin-proteasome dependent and independent degradation, and this would explain the inherent susceptibility to proteolysis among proteins containing PEST motifs. Considering RON9, we suggested that the PEST repetitions would be also subjected to proteolysis and that the successive digestions of the PEST sequences would explain the Staurosporine presence of lower bands of decreasing intensity and regular spacing present under the major band corresponding to RON9 in western blot. Whether RON9 is subjected in vivo to caspase Cycloheximide degradation or whether these bands correspond to degradation after lysis remains to be determined. RON9 also contains a Sushi domain. This domain is also present in TgRON1, which is the ortholog of the P. falciparum apical sushi protein PfASP1, also detected in the rhoptry neck. Finally, RON9 contains ankyrin repeats, which are the most common protein�Cprotein interaction motif in nature, and is predominantly found in eukaryotic proteins but also in pathogenic or symbiotic bacterial pathogens which deliver ANKcontaining proteins into eukaryotic cells through secretion systems, where they mimic or manipulate various host functions. The ankyrin repeat is a 33-residues motif that often occurs in tandem arrays, which cooperatively fold into structures that mediate molecular recognition via protein�Cprotein interactions and are involved in many cellular functions in eukaryotes, such as inhibition or development of tumors, transcriptional regulation, cell cycle, oncogenesis, signal transduction, and modulation of the inflammatory response mediated by NF-kB. Genomic analysis of viruses that infect eukaryotic cells has also revealed a large number of ank genes where they are implicated in host cell tropism and permissiveness. The presence of such repeats in RON9 suggests a potential interaction with host cell proteins upon invasion that remains to be explored. In order to address the function of RON9/RON10 complex in T. gondii, we have generated Dron9 parasites, which, based on RON10 mis-localization and degradation observations, likely corresponds to a RON9/RON102 phenotype. These parasites were not altered in HFF invasion capacity in vitro, neither in replication and tachyzoite virulence in vivo. Since neither RON9 nor RON10 are conserved across the Apicomplexa phylum, we had assumed that these proteins might not be involved in a crucial conserved mechanism shared by apicomplexan parasites. However, homologues of RON9 and RON10 have been detected in Eimeria spp., which could highlight a more specialized function for these proteins in the Coccidia. Orthologues have been also found in Cryptosporium spp., another apicomplexan parasite of humans and other vertebrates.