A Novel 66-kDa Stress Protein, p 66, Associated with the Process of Cyst Formation of Physarum polycephalum Is a Physarum Homologue of a Yeast Actin-Interacting Protein, AIP1

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When exposed to various stresses including heat shock, myxoamoebae, growing haploid cells of Physarum polycephalum, show marked morphological changes and consequently become disk-shaped microcysts. We have found that p 66 is induced exclusively in the course of microcyst formation and has an actin-binding activity. In this study, we purified p 66 to homogeneity and isolated a p 66 cDNA. The deduced protein sequence contained 601 amino acids and showed 31% identity to a yeast actin-interacting protein, AIP1. Northern blot analysis revealed that the amount of p 66 mRNA was significantly increased by heat shock in myxoamoebae but not in plasmodia. Thus, p 66 seems to be a developmentally-expressed stress protein which regulates the rearrangement of actin organization during microcyst formation P. polycephalum.