Characterization of two minicircular plasmid-like DNAs isolated from date-palm mitochondria

We report here the identification and characterization of two minicircular plasmid-like DNAs isolated from mitochondria of a moroccan date-palm variety. Both molecules were cloned and used as probes in Southern analyses of mitochondrial and total-cellular DNA. Evidence was obtained that these plasmid-like DNAs cross-hybridized but did not show any homology to nuclear, chloroplastic, or main mitochondrial genomes. Sequence analysis revealed that both minicircles, 1,346- and 1,160-bp long, share several stretches of homology, the most important consisting of three identical clusters of lengths 42, 47 and 38 bp. In contrast, no major homology was observed with the other higher-plant plasmid-like DNAs reported so far. Sequence analysis also revealed the presence, in the same strand of one of the minicircles, of two open reading frames potentially encoding proteins 89 and 86 amino acids in length. Interestingly, Northern analyses, using single strands of each minicircle as probes, showed the presence of two transcripts hybridizing only with the strand bearing these two open reading frames. However, computer-assisted comparison of the predicted polypeptide sequences with a protein-sequence library failed to detect any significant homology to known sequences.