Isolation of substances that stimulate RNA synthesis from red kidney bean: their activities in lymphocytes and Escherichia coli.

An extract from red kidney beans (Phaseolus vulgaris) was fractionated with respect to RNA synthesis-stimulating activity. The activity of the fractions was tested in chicken-spleen lymphocytes cultured in serum-free medium and in plasmolyzed E. coli cells. Lymphocyte-stimulating activity was found in a fraction called F III. This fraction contained protein and orcinol-positive carbohydrate. The protein (called F III p) responsible for the observed activity was separated from the contaminating carbohydrate by acid precipitation. F III p appears to belong to the group of well-known mitogens of high molecular weight present in red kidney beans. A bacteria-stimulating factor was found in a fraction called F V. This factor strongly stimulated RNA synthesis in the bacterial system, and had a weak stimulating effect in the lymphocyte system. In plasmolyzed E. coli cells, F V counteracted the inhibiting effect of rifampicin on RNA synthesis.