Abstract
Regulation of the EKI1-encoded ethanolamine kinase by inositol and choline was examined in Saccharomyces cerevisiae. Transcription of the EKI1 gene was monitored by following the expression of beta-galactosidase activity driven by a P(EKI1)-lacZ reporter gene. The addition of inositol to the growth medium resulted in a dose-dependent decrease in EKI1 expression. Supplementation of choline to inositol-containing growth medium brought about a further decrease in expression, whereas choline supplementation alone had no effect. Analysis of EKI1 expression in ino2Delta, ino4Delta, and opi1Delta mutants indicated that the transcription factors Ino2p, Ino4p, and Opi1p played a role in this regulation. Moreover, mutational analysis showed that the UAS(INO) element in the EKI1 promoter was required for the inositol-mediated regulation. The regulation of EKI1 expression by inositol and choline was confirmed by corresponding changes in ethanolamine kinase mRNA, protein, and activity levels. The repression of ethanolamine kinase by inositol supplementation correlated with a decrease in the incorporation of ethanolamine into CDP-ethanolamine pathway intermediates and into phosphatidylethanolamine and phosphatidylcholine.
Highlights
PE is synthesized by complementary pathways in S. cerevisiae [3, 12,13,14,15]
There is a lack of information regarding the regulation of expression of the genes encoding enzymes responsible for PE synthesis via the CDP-ethanolamine branch of the Kennedy pathway
Understanding the regulation of PE synthesis is important because it plays an essential role in yeast physiology when cells are grown with nonfermentable carbon sources [4, 5]
Summary
PE is synthesized by complementary pathways in S. cerevisiae (see Fig. 1) [3, 12,13,14,15]. The expression of genes encoding enzymes responsible for the synthesis of phosphatidylinositol (INO1) and PC (CDS1, CHO1/PSS1, PSD1, CHO2/PEM1, OPI3/PEM2, CKI1, and CPT1) is regulated by inositol [3, 12, 13, 22,23,24]. These genes are maximally expressed when inositol is absent from the growth medium and repressed when inositol is added to the growth medium. There is a lack of information regarding the regulation of expression of the genes encoding enzymes responsible for PE synthesis via the CDP-ethanolamine branch of the Kennedy pathway. The phospholipid synthesis regulatory proteins Ino2p, Ino4p, and Opi1p, and the UASINO cisacting element in the EKI1 promoter mediated the regulation of EKI1 expression
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