SYNTHESIS OF LIPID-LINKED OLIGOSACCHARIDES IS DEPENDENT ON THE CELL-CYCLE IN RAT 3Y1 CELLS

Synchronized cultures of rat 3Y1 cells, prepared by the density-arrest ed method, were used to investigate the relationship of N-glycosylatio n to the cell cycle, Although total cellular proteins were synthesized independently of the cell cycle, the synthesis of membrane-bound prot eins was found to be dependent on the cell cycle, the time of maximum synthesis being just before that of maximum DNA synthesis, The synthes is of lipid-linked oligosaccharides (LLO), which are utilized as inter mediates in N-glycosylation, increased in the S phase to a level at le ast ten times higher than in the G(1), G(2), and M periods, Moreover, the activities of dehydrodolichyl diphosphate synthase and farnesyl di phosphate synthase, which synthesize the precursors of dolichol, also increased in the S phase concomitantly with LLO synthesis. However, si nce the cell cycle dependency curves of these two enzyme activities we re somewhat broader than that of LLO synthesis, the rate-limiting enzy me in the regulation of LLO synthesis might be another one such as deh ydrodolichol reductase, These results suggest that LLO synthesis is re gulated by multiple synthetic enzymes which are activated in a cell cy cle-dependent manner.