Two Duplicated Genes DDI2 and DDI3 in Budding Yeast Encode a Cyanamide Hydratase and Are Induced by Cyanamide [Enzymology]

April 6th, 2015 by Li, J., Biss, M., Fu, Y., Xu, X., Moore, S. A., Xiao, W.

Two DNA damage-inducible genes in Saccharomyces cerevisiae, DDI2 and DDI3, are identical and encode putative HD domain-containing proteins, whose functions are currently unknown. Since Ddi2/3 also shows limited homology to a fungal cyanamide hydratase that converts cyanamide to urea, we tested the enzymatic activity of recombinant Ddi2. To this end, we developed a novel enzymatic assay and determined that the KM of the recombinant Ddi2/3 for cyanamide is 17.3 +/- 0.05 mM and its activity requires conserved residues in the HD domain. Unlike most other DNA damage-inducible genes, DDI2/3 is only induced by a specific set of alkylating agents and surprisingly is strongly induced by cyanamide. To characterize the biological function of DDI2/3, we sequentially deleted both DDI genes and found that the double mutant was unable to metabolize cyanamide and became much more sensitive to growth inhibition by cyanamide, suggesting that the DDI2/3 genes protect host cells from cyanamide toxicity. Despite the physiological relevance of the cyanamide induction, DDI2/3 is not involved in its own transcriptional regulation. The significance of cyanamide hydratase activity and its induced expression is discussed.