MINI-EXON GENE VARIATION IN HUMAN PATHOGENIC LEISHMANIA SPECIES

We have used polymerase chain reaction to amplify the mini-exon gene repeat from 18 Leishmania strains. DNA sequence analysis of the cloned products reveals high conservation of both the exon and intron (i.e. transcribed region). In contrast, variation is evident in both th length and primary sequence of the non-transcribed spacers. Dermotropic species of the New World subgenus Leishmania possess a 0.3-kb gene that differs from the 0.25-kb gene of New Wold dermotropic species of the subgenus Viannia. The Old/New World viscerotropic species and Old World dermotropic species posses a 0.4-kb mini-exon gene. However, the genes from the viscerotropic and dermotropic groups may be distinguished on the basis of sequence differences in the non-transcribed spacer. Comparative analysis of the -86 to -1 region from all species has been used to measure relatedness within the genus. In general, all the observed differences correlate with the four major groups of Leishmania (new World dermotropic Leishmania, New World dermotropic Viannia, Old World dermotropic Leishmania and viscerotropic Leishmania). Two of the three repeats cloned from L. donovani show short deletions. The missing sequence is flanked by direct, 7-bp repeats suggesting that the sequences may have been deleted by homologus recombination. Such rearrangements could account for the diversity detected in the non-transcribed spacers of the mini-exon genes.