ENDOGENOUS AUTOINHIBITORS REGULATE CHANGES IN ACTIN TYROSINE PHOSPHORYLATION DURING DICTYOSTELIUM SPORE GERMINATION

Phosphorylation of proteins on tyrosine residues has been shown to gov ern many cellular processes, but little work has focused on the role o f tyrosine phosphorylation during germination. Under optimal condition s, D. discoideum spores synchronously germinate each liberating a sing le amoeba. The total amount of phosphotyrosine containing proteins obs erved in spores was greatest during quiescence with a gradual decline during spore activation and emergence of nascent amoebae. During dorma ncy, tyrosine residues of actin were heavily phsophorylated, but they gradually underwent dephosphorylation upon spore activation and this p rocess continued through emergence. Interestingly, an endogenous autoi nhibitor(s), which blocks germination, induces tyrosine phosphorylatio n of actin. Conversely, the removal of the autoinhibitor(s) was follow ed by a decrease in phosphorylation. Thus, during germination of Dicty ostelium spores, actin is dephosphorylated, with the level of phosphor ylation regulated by the autoinhibitor(s) and/or the autoactivator. Th is change in actin phosphorylation appears to play a direct role since actin dephosphorylation and reorganization is a necessary prelude to germination. Copyright (C) 1997 Elsevier Science Inc.