Abstract
We have previously cloned cDNA encoding chloroplastic CuZn-superoxide dismutase (Chl CuZn-SOD) from Spirogyra and its amino acid sequence suggests that the Spirogyra enzyme is a branching point of Chl and cytosolic (Cyt) CuZn-SOD in plants. Here, we have isolated the genomic gene from Spirogyra. The clones (8 kbp) encoding Chl CuZn-SOD were obtained by PCRs. The algal gene sequenced for 3,402 bp contains nine exons and eight introns while plant Chl CuZn-SOD genes eight and seven, respectively. The exon/intron structure of the Spirogyra gene was the same as those of the plant Chl genes except for the first intron. The first intron (191 bp) locates at 9 bp upstream from the cleavage site of Chl transit peptide, which is identical site of the first intron in 5'-UTR of the plant Cyt genes. Thus, the Spirogyra gene seems to represent an ancestor for both types of CuZn-SOD.
