Phosphatidylcholine biosynthesis via the CDP-choline pathway is primarily regulated by CTP:phosphocholine cytidylyltransferase (CT). Transcriptional enhancer factor-4 (TEF-4) enhances the transcription of CT␣ in COS-7 cells by interactions with the basal tran scription machinery (Sugimoto, H., Bakovic, M., Yamashita, S., and Vance, D.E. (2001) J. Biol. Chem. 276, -12344). To identify the most important transcription factor involved in basal CT␣ transcription, we made CT␣ promoter-deletion and

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... utated constructs linked to a luciferase reporter and transfected them into COS-7 cells. The results indicate that an important site regulating basal CT␣ transcription is ؊53/؊47 (GACTTCC), which is a putative consensus-binding site of Ets transcription factors (GGAA) in the opposite orientation. Gel shift analyses indicated the existence of a binding protein for ؊53/؊47 (GACTTCC) in nuclear extracts of COS-7 cells. When anti-Ets-1 antibody was incubated with the probe in gel shift analyses, the intensity of the binding protein was decreased. The binding of endogenous Ets-1 to the promoter probe was increased when TEF-4 was expressed; however, the amount of Ets-1 detected by immunoblotting was unchanged. When cells were transfected with Ets-1 cDNA, the luciferase activity of CT␣ promoter constructs was greatly enhanced. Co-transfection experiments with Ets-1 and TEF-4 showed enhanced expression of reporter constructs as well as CT␣ mRNA. These results suggest that Ets-1 is an important transcriptional activator of the CT␣ gene and that Ets-1 activity is enhanced by TEF-4. Phosphatidylcholine (PC) 1 is the major membrane phospholipid in mammalian cells and tissues. PC is made in all nucle-*