Modulation in the rates of incorporation of lipid precursors during the cell cycle

The rates of incorporation of 3 H‐choline into phospholipid and of 3 H‐fucose into glycolipid have been measured during the cell cycle of the murine mastocytoma, P815Y, synchronized by either velocity sedimentation or excess thymidine blockade. The rate of 3 H‐choline incorporation into acid‐insoluble material exhibited two distinct maxima coincident with the early S and G 2 periods, whereas the rate of incorporation of 3 H‐fucose into lipid extractable material was maximal during the G 2 period. Variation in rate of incorporation of 3 H‐choline could not be accounted for by changes in membrane permeability.