Figure 6.

Mis-splicing of exons b and c occurs in wheat but not Oenothera. (A) Upper: products of b to c splicing in wheat (left) and Oenothera (right) as analyzed by RT–PCR using primers that anneal downstream of exon c and within exon b. Primers specific to wheat mtRNA are indicated with the ‘wh’ prefix, those specific to Oenothera with the ‘oe’ prefix and primers suitable for use on both templates are indicated with the ‘wo’ prefix. All products were individually cloned and sequenced to determine the identity of the sequences within them. Regions of exon b that are missing in one or more of the analyzed products are indicated by hatched lines. Only a single product, consisting of exon b correctly spliced to exon c was obtained from Oenothera. Mis-spliced products predominated in wheat mtRNA; mis-splicing occurred at sites corresponding to those of Brassica. The smallest wheat excision product, corresponding to the properly spliced intron, is not shown. Lower: excision products of b to c mis-splicing (wheat) splicing in (Oenothera). Multiple products, corresponding to Y-shaped excision products derived from mis-splicing, are observed in wheat mitochondria (left), whereas only a single product, corresponding to the excised intron, is observed in Oenothera mitochondria (right). (B) Upper: splicing of exons c and d in wheat and Oenothera; as in Brassica, only a single RT–PCR product, corresponding to a properly spliced mRNA, is observed. Lower: only a single excision product, corresponding to the correctly spliced intron is observed in both wheat and Oenthera.