CONCERTED EVOLUTION AT A MULTICOPY LOCUS IN THE PROTOZOAN PARASITE THEILERIA-PARVA - EXTREME DIVERGENCE OF POTENTIAL PROTEIN-CODING SEQUENCES

Concerted evolution of multicopy gene families in vertebrates is recog nized as an important force in the generation of biological novelty bu t has not been documented for the multicopy genes of protozoa, A multi copy locus, Tpr, which consists of tandemly arrayed open reading frame s (ORFs) containing several repeated elements has been described for T heileria parva, Herein we show that probes derived from the 5'/N-termi nal ends of ORFs in the genomic DNAs of T. parva Uganda (1,108 codons) and Boleni (699 codons) hybridized with multicopy sequences in homolo gous DNA but did not detect similar sequences in the DNA of 14 heterol ogous T. parva stocks and clones, The probe sequences were, however, p rotein coding according to predictive algorithms and codon usage, The 3'/C-terminal ends of the Uganda and Boleni ORFs exhibited 75% similar ity and identity, respectively, to the previously identified Tpr1 and Tpi2 repetitive elements of T. parva Muguga, Tpr1-homologous sequences were detected in two additional species of Theileria. Eight different Tpr1-homol ogous transcripts were present in piroplasm mRNA from a si ngle T. parva Muguga-infected animal, The Tpr1 and Tpr2 amino acid seq uences contained six predicted membrane-associated segments, The ratio of synonymous to nonsynonymous substitutions indicates that Tpr1 evol ves like protein-encoding DNA, The previously determined nucleotide se quence of the gene encoding the p67 antigen is completely identical in T. parva Muguga, Boleni, and Uganda, including the third base in codo ns, The data suggest that concerted evolution can lead to the radical divergence of coding sequences and that this can be a mechanism for th e generation of novel genes.