Characterisation of a cluster of genes encoding Theileria annulata AT hook DNA-binding proteins and evidence for localisation to the host cell nucleus.

Infection of bovine leukocytes by the apicomplexan parasite Theileria annulata results in alteration of host cell gene expression and stimulation of host cell proliferation. At present, the parasite-derived factors involved in these processes are unknown. Recently, we described the characterisation of a parasite gene (TashAT2), whose polypeptide product bears AT hook DNA-binding motifs and may be transported from the parasite to the host nucleus. We now describe the isolation of a further two genes (TashAT1 and TashAT3) that are very closely related to TashAT2. All three TashAT genes are located together in a tight cluster, interspersed by two further small open reading frames, all facing head to tail. TashAT2 was shown to be expressed in all T. annulata cell lines examined, whereas TashAT1 and TashAT3 were expressed in the sporozoite stage of the parasite, and also in infected cell lines, where their expression was found to vary between different cell lines. Evidence for transport was provided by antisera raised against TashAT1 and TashAT3 that reacted with the host nucleus of T. annulata-infected cells. Reactivity was particularly strong against the host nuclei of the T. annulata-infected cloned cell line D7B12, which is attenuated for differentiation. A polypeptide in the size range predicted for TashAT3 was preferentially detected in host enriched D7B12 nuclear extracts. DNA-binding analysis demonstrated that fusion proteins containing the AT hook region of either TashAT1 or TashAT2 bound preferentially to AT rich DNA.