Actin of Naegleria gruberi. Absence of N tau-methylhistidine.

Actin from amebae of Naegleria gruberi has been purified to homogeneity. The purified actin shares many attributes with numerous other actins that have been characterized, including molecular weight, strong binding to DEAE-cellulose, binding to DNase I, reversible polymerization to F-actin, binding of rabbit myosin subfragment 1 to give distinctive arrowheads , formation of Mg paracrystals, and activation of myosin Mg2+-ATPase. In two respects the attributes of Naegleria actin are unusual. Isoelectric focusing resolves three distinct isoforms of the actin, which raises questions about the function of multiple isoforms in a unicellular eukaryote. The amino acid composition closely resembles other actins except that Naegleria actin lacks N tau-methylhistidine. This result indicates that N tau-methylhistidine is not a prerequisite for actin-actin or actin-myosin interactions.