THE MITOCHONDRIAL NAD5 GENE OF SUGAR-BEET (BETA-VULGARIS) ENCODING A SUBUNIT OF THE RESPIRATORY NADH DEHYDROGENASE

We have isolated the nad5 gene from the N-cytoplasm of Beta vulgaris, by heterologous hybridization with a nad5 probe from Chlamydomonas reinhardtii, and have determined the DNA sequence. The gene has a length of 3082 bp and consists of three exons and two introns, 459, 1269, 270, 848 and 357 bp in length, respectively. It has a similarity of 95.1% at the DNA level to the nad5 gene of Oenothera and the two respective proteins show an overall level of amino acid identity of 88.7%. Compared to Oenothera the reading frame of the first exon is extended in the 5′ direction and in the third exon there is a frameshift shortening the reading frame by 96 bp and changing the last 48 codons. The nad5 gene is a single copy gene in the N- and S-cytoplasm of Beta vulgaris and the organisation of the gene shows no apparent differences in the two cytoplasms. The gene is actively expressed; three major transcripts are detectable. The transcript patterns have been compared between the two cytoplasms and between different plant tissues. © 1990 Springer-Verlag.