Low levels of exogenous histone H1 in yeast cause cell death.

To elucidate the function of lysine-rich histone, yeast cells, which are believed to lack this histone, were transformed with an expression vector carrying the sea urchin histone H1 gene under control of an inducible promoter. Expression of full-length protein was tested by immunoblotting and the intracellular distribution was monitored by immunoelectron microscopy. Even low amounts of exogenous H1 led to dramatic changes in intracellular morphology and cell death. The cells that survived had lost either the plasmid or the ability to express the exogenous protein. Thus, even low amounts of canonical histone H1 are lethal to yeast cells.