Choline kinase from yeast.

Choline kinase, the initial enzyme of the CDP-choline pathway, mediates the conversion of choline to phosphorylcholine and is localized in the supernatant fraction of cells. The enzyme also catalyzes the phosphorylation of ethanolamine, functioning as the initial enzyme of the CDP-ethanolamine pathway as well. Yeast choline kinase is encoded by a single structural gene, CKI, which was cloned by the genetic complementation of the choline kinase mutation cki. The deduced sequence comprises 582 amino acid residues with a molecular mass of 66316 Da and bears local sequence similarity to various protein kinases and bacterial antibiotic phosphotransferases. The expression of yeast choline kinase is transcriptionally repressed by myo-inositol and choline in a coordinate manner with other phospholipid-synthesizing enzymes in yeast.