STRESS-INDUCED TYROSINE PHOSPHORYLATION OF ACTIN IN DICTYOSTELIUM CELLS AND LOCALIZATION OF THE PHOSPHORYLATION SITE TO TYROSINE-53 ADJACENT TO THE DNASE-I BINDING LOOP

Actin is known to be phosphorylated at tyrosine, serine, or threonine residues in various cells, In cells of Dictyostelium discoideum, a ris e in the tyrosine phosphorylation of actin is observed in response to ATP depletion, An actin fraction rich in phosphotyrosine was obtained by chromatography on the weak anion exchanger Mono-P, Mass spectrometr y and amino acid sequencing of protease cleavage products indicated th at a single tyrosine residue was phosphorylated. Localization of this residue to position 53 of the actin sequence attributed the modificati on to a site that is critical for the capability of actin to polymeriz e. Induction of the tyrosine phosphorylation by heat shock and Cd2+ io ns indicates that this modification of actin is implicated in the resp onse of Dictyostelium cells to stress.