MINI-EXON GENE VARIATION IN HUMAN PATHOGENIC LEISHMANIA SPECIES

We have used polymerase chain reaction to amplify the mini-exon gene r epeat from 18 Leishmania strains. DNA sequence analysis of the cloned products reveals high conservation of both the exon and intron (i.e. t ranscribed region). In contrast, variation is evident in both th lengt h and primary sequence of the non-transcribed spacers. Dermotropic spe cies of the New World subgenus Leishmania possess a 0.3-kb gene that d iffers from the 0.25-kb gene of New Wold dermotropic species of the su bgenus 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. Comp arative analysis of the -86 to -1 region from all species has been use d to measure relatedness within the genus. In general, all the observe d 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 thre e repeats cloned from L. donovani show short deletions. The missing se quence is flanked by direct, 7-bp repeats suggesting that the sequence s may have been deleted by homologus recombination. Such rearrangement s could account for the diversity detected in the non-transcribed spac ers of the mini-exon genes.