Characterization of a spore protein inducing factor from Dictyostelium discoideum

Spore coat protein synthesis during development by submerged pseudoplasmodia of Dictyostelium discoideum requires a low molecular weight factor secreted by cells incubated at high density inbuffer. The further characterization of this sporeprotein inducing factor (SPIF) is reported. Its behaviour during anion-exchange chromatography and the loss of activity upon esterification suggests the presence of a carboxylic acid group essential for biological activity. Gel permeation chromatography resolves a major SPEF activity with Mr ∼ 160–200 and a minor activity with Mr ∼ 340–420. Anion-exchange HPLC further resolves the major SPIF activity into four components, one major and three minor. Methionine, analogues of methionine, and precursors of methioninebio synthesis are all effective in maintainingspore coat protein synthesis. Condition edmedium contains methionine at a concentration sufficient to account for its SPIF activity and this activity is abolished by cyanogen bromide treatment. These results indicate that SPIF is eithermethionine or a close analogue of methionine.