THE USE OF A MITOCHONDRIAL (MT) GENE LIBR ARY FOR CHARACTERIZATION OFMT GENOMES AND THE SEARCH OF NEW MT GENES IN HIGHER-PLANTS

The mt genome of higher plants (size varying from 200 to 560 kb accord ing to the species) consists of a heterogeneous population of molecule s resulting from intra- or inter-molecular recombination. Besides the highly conserved coding sequences of mt genes, other sequences, for ex ample, promiscuous chloroplast sequences, may be found. The genes may be interrupted by introns; in some cases, one or more introns have bee n split, leading to the scattering of the gene segments to remote part s of the genome; this structure requires trans-splicing steps for the mature messenger RNA to be obtained. Over 25 genes have been identifie d so far that are usable, as universal polymorphism markers in RFLP (r estriction fragment length polymorphism) characterization of mt genome s due to sequence conservation. During the search for new genes we ide ntified 2 new coding sequences, nad5 and nad6; nad6 consists of a sing le reading frame whereas nad5 is a split gene whose 3 independent segm ents are independently transcribed.