Expression of ras-family genes in the cell cycle and during differentiation of the lower eukaryote Physarum polycephalum.

Messenger RNA levels of three ras-family genes (Ppras1, Ppras2, and Pprap1) were measured in different life forms and throughout the cell cycle of the slime mold Physarum polycephalum. All three genes are expressed at constant rates in the uninucleate amoebae and flagellates, regardless of the culture conditions (solid or liquid medium, particulate or dissolved nutrients). In the multinucleate stages (micro- and macroplasmodia) Ppras1 and Pprap1 mRNAs are somewhat less abundant, while Ppras2 is not expressed at all. The early stages of the amoeba-plasmodium transition proceed without any drop in Ppras2 expression. During the synchronous cell cycle in macroplasmodia Ppras1 and Pprap1 are expressed at a constant level.