Localization of PtdIns4P at the Golgi and PM. (A) Left and center: Confocal images of YFP-tagged P4M and CFP-tagged giantin serving as PtdIns4P and Golgi indicators, respectively. Right: Overlay of P4M (green) and giantin (red). Scale bar, 10 µm. (B) Fractional partitioning of P4M-YFP fluorescence between the Golgi and PM. z-Stacks of confocal images were integrated to estimate relative P4M near the Golgi and near the PM (see Materials and methods). n = 9 cells. F/Ftotal, integrated fluorescence in the Golgi or PM divided by the total fluorescence in the cell.