Secretion of invertase in mitotic yeast cells

In mammalian cells intracellular transport is inhibited during mitosis. Here we show that in the yeast Saccharomyces cerevisiae secretion continues uninterrupted during mitosis. S. cerevisiae cells were arrested in mitosis by treating wild-type cells with the microtubule-inhibitor nocodazole, or by incubating a temperature-sensitive cell division cycle mutant (cdc16) at the restrictive temperature. Secretion of invertase into the periplasmic space was equally efficient in mitotic and in unsynchronized cells. Electron microscopy of nocodazole-treated mitotic wild-type cells revealed stretches of rough endoplasmic reticulum, strongly fenestrated Golgi cisternae and clusters of vesicles with the diameter of 30-90 nm. Secretion of invertase was inhibited in mitotic sec7 cells at the restrictive temperature, but continued at the permissive temperature. Sec7 is a mutant strain where intracellular traffic is blocked in unsynchronized cells in the Golgi complex at the restrictive temperature. Thus, the elements of the mitotic Golgi complex appear to be able to support intracellular traffic.