Variation in copy number of a 24-base pair tandem repeat in the chloroplast DNA of Oenothera hookeri strain Johansen

A highly variable region of chloroplast DNA has been analyzed from three isolates of Oenothera hookeri strain Johansen. The variability results from the presence of two, four or seven copies of a discrete 24-base pair tandem repeat in a segment of the chloroplast DNA within the inverted repeat. Alignment of this DNA region with the published tobacco cpDNA sequence shows that in Oenothera, the repeats are insertions within a large unidentified reading frame, with each repeat unit specifying an eight amino acid in-frame addition. A model to explain the frequent alterations in the copy number of this 24-bp unit is proposed: imprecise alignment and recombination between the two large inverted repeats followed by copy correction could result in an amplification or deletion of the 24-bp segments.