Acetylated and nonacetylated actins in Dictyostelium discoideum.

We have carried out a two-dimensional gel analysis of the actin system of Dictyostelium discoideum. Our results show that on the basis of isoelectric focusing, there is a single major [35S]methionine-labeled species which corresponds both to the actin purified by Uyemura et al. (Uyemura, D., Brown, S.S., and Spudich, J.A. (1978) J. Biol. Chem. 253, 9088-9095) and to the Coomassie Blue staining species seen in whole cell lysates of the organism. We also detect a minor labeled actin species, x, which has no corresponding Coomassie Blue staining counterpart. This species turns over much more rapidly than the major actin and has one more positive charge. It is not labeled with [3H]acetate, whereas the major actin is. When D. discoideum RNA is added to a mRNA-dependent rabbit reticulocyte lysate protein translation system, only one major actin is seen, and this species corresponds to the major actin observed in vivo. If endogenous acetyl coenzyme A is removed from the translation system, a second major actin appears corresponding in position to x. These results indicate that in D. discoideum, there is present a single major actin species in addition to a small amount of a rapidly turning over actin which is a nonacetylated form of the major actin. Additional experiments examining these actins through the developmental cycle of the organism show no consistent differences with the results obtained using vegetative cells.