Characterization of a cDNA encoding a novel subunit for cytochrome c oxidase (COX6b) from rice

To date, there have been only a limited number of reports about the nuclear-encoded subunit for cytochrome c oxidase (COX) in the mitochondria of higher plants. In the present study, we characterized a cDNA encoding a novel subunit of COX (COX6b), which had not previously been reported in plants, It was found that the rice COX6b gene encodes 169 amino acids with a calculated molecular mass of 19 kDa. The deduced amino acid sequence of rice COX6b is longer than those of vertebrate and yeast COX6b subunits. Genomic Southern hybridization suggested that the rice COX6b subunit is encoded by at least two copies of COX6b genes. Northern hybridization showed that one of the genes (COX6B-1) is constitutively transcribed in different organs of rice. However, the steady-state mRNA levels slightly varied among organs.