Sequences of six genes and several open reading frames in the kinetoplast maxicircle DNA of Leishmania tarentolae

Abstract

The DNA sequence of approximately 80% of the transcribed region of the kinetoplast maxicircle DNA of Leishmania tarentolae was obtained, and structural genes were localized by comparison of the translated amino acid sequences with those of known mitochondrial genes from other organisms. By this method, the genes for cytochrome oxidase subunits I, II, and III, cytochrome b, and human mitochondrial unidentified reading frames 4 and 5 were identified. By comparing the amino acid sequences of the putative L. tarentolae genes with those of known genes, we conclude that TGA codes for tryptophan, as in most other mitochondrial systems. This is the only apparent change from the universal genetic code. The six identified structural genes show various degrees of divergence from the homologous genes in other species, with cytochrome oxidase subunit I being the most conserved and cytochrome oxidase subunit III being the least conserved. A comparison of the cytochrome b genes from L. tarentolae and Trypanosoma brucei showed that the ratio of transversions to transitions is 1:1, suggesting that these species diverged from each other more than 80 X 10(6) years ago. Several as yet unidentified open reading frames were also present in the maxicircle sequence. These data confirm that maxicircle DNA has a coding potential which typifies other mitochondrial systems.