Histone proteins in vivo: Cell-cycle-dependent physiological effects of exogenous linker histones incorporated into Physarum polycephalum

We detail a method which allows biochemical quantities of histone proteins to be introduced into a living eukaryotic cell. This method involves absorp tion of purified proteins into macroplasmodia of Physarum polycephalum. Fur ther, since Physarum macroplasmodia exist as syncitial culture with complet ely synchronous nuclei with respect to cell cycle events, proteins may be I ntroduced at specific points during the eukaryotic cell cycle. We show that a linker histone is absorbed whole into these cells and are property trans ported to the nuclei of the cell. Furthermore, we also show incorporation o f linker histone H5 inhibits the transcriptional activities occuring during the G(2) phase in Physarum. This method wilt make it possible to introduce histones modified with structural probes into chromatin naturally assemble d in vivo. (C) 1999 Academic Press.