Molecular Cloning of a cDNA that Encodes a Spinach Cysteine Synthase-Like Protein

In Spinacia oleacea, three isoforms of cysteine synthase (CSase, O-acetyl-serine (thiol) lyase) were identified in the cytosolic, plastidial, and mitochondorial compartments. Here, we report molecular cloning of a cDNA that encodes a CSase-like protein, designated CSaseLP. The predicted amino acid sequence of CSaseLP showed high identity (about 70%) with that of a spinach cytosolic CSase (encoded by CSaseA gene). The CSase activity of recombinant CSaseLP was barely detectable. The antibody raised against the recombinant CSaseLP protein recognized weakly a recombinant CSaseA protein. Northern blot analysis showed that CSaseLP gene was expressed mainly in root tissues, while the expression of CSaseA gene was constitutive in leaf and root tissues. These results suggest that the CSaseLP protein, though belongs to the CSase family, play a role distinct from the cytosolic CSase.