ACTIVE TRANSCRIPTION OF THE PSEUDOGENE FOR SUBUNIT-7 OF THE NADH DEHYDROGENASE IN MARCHANTIA-POLYMORPHA MITOCHONDRIA

A pseudogene, psi nad7, which has significant sequence similarity (66. 7% amino acid identity) with the bovine nuclear gene for a 49 kDa subu nit of the NADH dehydrogenase (NADH:ubiquinone oxidoreductase, EC 1.6. 99.3), has been identified on the mitochondrial genome of the liverwor t Marchantia polymorpha. The predicted coding region, which includes s ix termination codons, is actively transcribed into RNA molecules of 1 6 and 9.6 kb in length, but RNA splicing products were not detected in the liverwort mitochondria. Genomic DNA blot analysis and RNA blot an alysis using poly(A)(+) RNA suggest that a structurally related nuclea r gene encodes the mitochondrial ND7 polypeptide. These results imply that this psi nad7 is a relic of a gene transfer event from the mitoch ondrial genome into the nuclear genome during mitochondrial evolution in M. polymorpha.