Identification of cAMP-dependent phosphorylated proteins involved in the formation of environment-resistant resting cysts by the terrestrial ciliate Colpoda cucullus

In the terrestrial ciliate Colpoda cucullus, an elevation of the intracellular cAMP concentration was reported to be involved in environment-resistant resting cyst formation. In the present study, cAMP-dependently phosphorylated proteins of encystment-induced C. cucullus were isolated with Phos-tag agarose phosphate-affinity beads and subsequent SDS-PAGE. In a liquid chromatography/tandem mass spectrometry analysis of these phosphoproteins, 27-, 37- and 43-kDa proteins (p27, p37 and p43) were identified as Rieske iron-sulfur protein, histone H4 (hyperacetylated form), and actin, respectively.