Inhibition of the synthesis of a cytochrome‐c‐oxidase subunit isoform by antisense RNA

To investigate the role of subunit VIIe, an oxygen‐regulated subunit isoform of Dictostelium discoideum cytochrome‐c oxidase, the full‐length cDNA was inserted into an expression vector under the control of an actin promoter in the sense and antisense orientation. The DNA constructs were used for stable transformation of the slime mold amoebae. In most of the 28 antisense clones tested, the concentration of cytochrome‐c oxidase was lowered compared to the wild type, while no significant changes were found in the sense mutants. Antisense RNA was abundantly expressed, leading to a drastic reduction of the steady‐state level of the endogenous subunit VIIe mRNA, which was decreased up to 20–30% the level observed in parent cells. In these transformants, the amount of the target polypeptide and cytochrome c oxidase was 40–50% and 60–70% of control, respectively. A similar decrease was found in the level of the remaining nuclear and mitochondrial subunits. Unexpectedly, these changes affecte...