CISSPLICING AND TRANSSPLICING AND RNA EDITING ARE REQUIRED FOR THE EXPRESSION OF NAD2 IN WHEAT MITOCHONDRIA

In wheat mitochondria, the gene coding for subunit 2 of the NADH-ubiqu inone oxidoreductase (nad2) is divided into five exons located in two distant genomic regions. The first two exons of the gene, a and b, lie 22 kb downstream of exons c, d, and e, on the same DNA strand. All in trons of nad2 are group II introns. A trans-splicing event is required to join exons b and c. It involves base pairing of the two precursor RNAs in the stem of domain IV of the intron. A gene coding for tRNA(Ty r) is located upstream of exon c. In addition to splicing processes, m RNA editing is also required for the correct expression of nad2. The m ature mRNA is edited at 36 positions, distributed over its five exons, resulting in 28 codon modifications. Editing increases protein hydrop hobicity and conservation.