Isolation of a gene encoding cysteine synthase from Flavobacterium K3-15

The cysteine synthase gene (cysK) from Flavobacterium K3-15 was cloned and sequenced. The gene exhibits 30-50% identity to known cysteine synthases on both the DNA and the amino acid levels. The pyridoxal phosphate binding site of the enzyme is part of a conserved motif comprising seven amino acids (SIKDRIA). The lys31 residue of the flavobacterial enzyme is conserved in all known cysteine synthases. The cysK gene from Flavobacterium K3-15 was heterologously expressed and the gene product identified by immunoblotting and determination of the enzyme activity.