Cloning and characterization of a cDNA encoding the chloroplastic copper/zinc-superoxide dismutase from pea.

A cDNA encoding the chloroplastic copper/zinc-superoxide dismutase of pea (Pisum sativum L.) was isolated from a cDNA library constructed in lambda gt11 from leaf mRNA. Nucleotide sequence analysis of the 875-base-pair clone revealed that it contained the complete coding sequence of the mature superoxide dismutase isozyme subunit, along with sequence information for a 48-amino acid N-terminal transit peptide. The deduced amino acid sequence of the mature subunit proved to be 64-87% homologous with amino acid sequences of copper/zinc-superoxide dismutases from other plant species. In vitro transcription, followed by cell-free translation, of the cDNA resulted in the formation of a 23.5-kDa precursor polypeptide, which, upon incubation with isolated pea chloroplasts, was imported and processed to its mature subunit molecular mass of 17.4 kDa.