THE COX1 GENE FROM EUGLENA-GRACILIS - A PROTIST MITOCHONDRIAL GENE WITHOUT INTRONS AND GENETIC-CODE MODIFICATIONS

We present the nucleotide sequence of the cox 1 gene encoding subunit 1 of cytochrome c oxidase in Euglena gracilis, the first report on a m itochondrial gene from this protist. Its study reveals that the Euglen a mitochondrial genome does not appear as a compact and homogeneous st ructure and that its A+T content is high (about 76%) whereas this valu e is less than 50% in nuclear DNA. The Euglena cox1 gene does not exhi bit any intron, and an amino-acid alignment of Euglena COX1 with homol ogous proteins shows that the universal genetic code is used. Comparis ons of the genomic and cDNA sequences of Euglena cox1 indicate that th e transcript does not undergo RNA editing as found in trypanosomes and in higher plants. The phylogeny obtained with COX1 protein sequences is in agreement with that obtained with nuclear rRNA sequences and pla ces Euglena and Trypanosoma far apart from other eukaryotes. This resu lt strengthens the hypothesis that these protists represent the earlie st mitochondrion-containing organisms.