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The Saccharomyces cerevisiae Phosphatidylinositol-Transfer Protein Effects a Ligand-Dependent Inhibition of Choline-Phosphate Cytidylyltransferase Activity

Henry B. Skinner, Todd P. McGee, Christopher R. McMaster, Michelle R. Fry, Robert M. Bell and Vytas A. Bankaitis
Proceedings of the National Academy of Sciences of the United States of America
Vol. 92, No. 1 (Jan. 3, 1995), pp. 112-116
Stable URL: http://www.jstor.org/stable/2366509
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Saccharomyces cerevisiae Phosphatidylinositol-Transfer Protein Effects a Ligand-Dependent Inhibition of Choline-Phosphate Cytidylyltransferase Activity
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Abstract

The Saccharomyces cerevisiae protein SEC14p is required for Golgi function and cell viability in vivo. This requirement is obviated by mutations that specifically inactivate the CDP-choline pathway for phosphatidylcholine biosynthesis. The biochemical basis for the in vivo relationship between SEC14p function and the CDP-choline pathway has remained obscure. We now report that SEC14p effects an in vivo depression of CDP-choline pathway activity by inhibiting choline-phosphate cytidylyltransferase (CCTase; EC 2.7.7.15), the rate-determining enzyme of the CDP-choline pathway. Moreover, this SEC14p-mediated inhibition of CCTase was recapitulated in vitro and was saturable. Finally, whereas the SEC14p-dependent inhibition of CCTase in vitro was markedly reduced under assay conditions that were expected to increase levels of phosphatidylinositol-bound SEC14p, assay conditions expected to increase levels of phosphatidylcholine-bound SEC14p resulted in significant potentiation of CCTase inhibition. The collective data suggest that the phosphatidylcholine-bound form of SEC14p effects an essential repression of CDP-choline pathway activity in Golgi membranes by inhibiting CCTase and that the phospholipidbinding/exchange activity of SEC14p represents a mechanism by which the regulatory activity of SEC14p is itself controlled.

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