Purification and identification of a growth factor produced by Paramecium tetraurelia

We previously reported that the jumyo mutant of a cilate protozoan Paramecium tetraurelia excretes into the medium a factor which promotes its own cell division. Here, the factor was purified to electrophoretic homogeneity through a series of liquid chromatographic procedures. This substance is a protein with a molecular weight of 17,000 which at concentrations of 1 X 10(-9) M (17 ng/ml) or more results in the recovery of the cell division rate of the jumyo mutant to the level of the wild type. The factor is therefore considered to be a growth factor and was named Paramecium growth factor (ParGF). This is the first report of direct proof for the production of a growth factor in an organism other than vertebrates.