Molecular characterization and functional analysis of subunit 7 of eukaryotic initiation factor 3 from Eimeria tenella.

The initiation of translation in eukaryotic cells is stimulated by proteins known as initiation factors (eIFs). A structurally complex eIF composed of multiple subunits, eIF3 has been shown to have various functions in translation in a variety of eukaryotes. Until now, little is known about eIF3 in Eimeria tenella. Based on a previously identified expressed sequence tag(EST), we cloned the eIF3 subunit 7 gene (EteIF3s7) from E. tenella by rapid amplification of the cDNA ends(RACE). The 2278-bp full-length complementary DNA of EteIF3s7 contained a 1716-bp open reading frame (ORF) that encoded a 571-amino acid (aa) polypeptide. The EteIF3s7 protein contained the subunit 7 domain that is characteristic of members of the eIF3 zeta superfamily. The levels of EteIF3s7 messenger RNA and protein were higher in second generation merozoites than in sporulated oocysts, unsporulated oocysts, or sporozoites, and the EteIF3s7 protein was barely detectable in unsporulated oocysts. Our immunofluorescence analysis showed that the EteIF3s7 protein was uniformly distributed throughout the cytoplasm of sporozoites. After sporozoites were incubated in complete medium, the EteIF3s7 protein localized to the anterior region of the parasite. Following the first schizogenous division, the protein was uniformly dispersed in trophozoites, immature schizonts, and mature schizonts, and the EteIF3s7 protein was observed to be closely associated with the parasitophorous vacuole membrane. An anti-rEteIF3s7 polyclonal antibody inhibited the ability of E. tenella to invade DF-1 cells, which suggested that EteIF3s7 might be involved in host cell invasion and required for the growth of the parasite in the host.