Regulation of theSaccharomyces cerevisiae CKI1-encoded Choline Kinase by Zinc Depletion

In the yeast Saccharomyces cerevisiae, the CKI1-encoded cho- line kinase catalyzes the committed step in the synthesis of phosphatidylcholine via the CDP-choline branch of the Kennedy pathway. Analysis of a PCKI1-lacZ reporter gene revealed that CKI1 expression was regulated by intracellular lev- els of the essential mineral zinc. Zinc depletion resulted in a concentration-dependent induction of CKI1 expression. This regulation was mediated by the zinc-sensing and zinc-inducible transcriptional activator Zap1p. A purified Zap1p probe inter- acted with two putative UASZRE sequences (ZRE1 and ZRE2) in the CKI1 promoter. Mutations of ZRE1 and ZRE2 to a noncon- sensus UASZRE attenuated the induction of CKI1 expression in response to zinc depletion. A UASINO element in the CKI1 pro- moter was responsible for stimulating CKI1 expression, but this element was not involved with the regulation by zinc depletion. The induction of CKI1 expression in zinc-depleted cells trans- lated into increased choline kinase activity in vitro and in vivo, and an increase in phosphatidylcholine synthesis via the Kennedy pathway. Recent studies have uncovered a novel relationship between the control of zinc homeostasis and the regulation of mem- brane phospholipid synthesis in the yeast Saccharomyces cer- evisiae (1). Zinc is an essential mineral for the growth and metabolism of S. cerevisiae; it serves as a cofactor for hundreds of enzymes and it is a structural component of several tran- scription factors (2- 4). The membrane function of zinc trans- port plays a central role in controlling the cellular levels of zinc (5). Zinc transporters are found in the plasma membrane (e.g. Zrt1p, Zrt2p, and Fet4p) (6 - 8), and membranes of the endo-