UBC Theses and Dissertations
Identification of Leishmania genes encoding proteins containing tandemly repeating peptides Wallis, Anne Elizabeth
In order to identify Leishmania proteins which may be immunologically relevant or may play a role in interactions between Leishmania and its mammalian host, a Leishmania major genomic DNA library was constructed in the vector λgt11 and screened with antibodies raised to Leishmania major promastigote membranes. Two recombinant DNA clones were identified which encoded repetitive sequences (Clone 20 and Clone 39). Clone 20 encoded a repetitive peptide of 14 amino acids and clone 39 encoded an unrelated repetitive peptide of 10 amino acids. Analysis of one of these clones, Clone 20, indicated that there were two RNA transcripts of 9500 and 5200 nucleotides expressed which corresponded to this clone in Leishmania major and Leishmania donovani and this expression was not stage-specific. The results of genomic DNA analysis and isolation of additional clones encoding Clone 20 sequences indicated that there were two genes which corresponded to Clone 20 in both Leishmania major and Leishmania donovani and that these genes differed from one another with respect to the number of repeats which they contained. Antibodies against the fusion protein produced by Clone 20 recognized a series of Leishmania major proteins of apparent mol wt 250,000. Analysis of Clone 39 indicated that there was a single transcript of 7500 nucleotides expressed which corresponded to this clone in both Leishmania major and Leishmania donovani and that there was a single gene (or two identical genes) which encoded this transcript. The genomes of many protozoan parasites exhibit a high degree of plasticity with respect to chromosome size and number. The presence of highly repetitive regions within their DNA may be involved in maintaining this plasticity, allowing the parasite to evolve rapidly under selective pressure. Repetitive regions have been identified within many Plasmodia antigens and have been implicated in the ability of this parasite to evade the host immune system. The presence of Leishmania genes encoding proteins containing tandemly repeating peptides may indicate that these proteins play a similar role in evading the host immune system during the course of Leishmania infections. The possible evolution and functions of repetitive proteins in protozoan parasites is discussed.