By screening for genes with homology to yeast Ste20 and mammalian PAK, key cytoskeleton regulators, Chung and Firtel (page 559) identified and characterized a putative PAK-family gene in Dictyostelium. The results are the first identification of an essential role of a putative PAK in cytokinesis, and the new gene, PAKa, also appears to regulate myosin II function during chemotaxis.
PAKa colocalizes with myosin II to the cleavage furrow of dividing cells and the posterior of chemotaxing cells, and paka null cells are defective in myosin II assembly. Cells lacking PAKa, or producing a putative dominant-negative form of the protein, produce random lateral pseudopodia during chemotaxis and also fail to undergo cytokinesis in suspension. The assembly of myosin II into the cytoskeleton is also defective in paka null cells, but PAKa does not phosphorylate myosin II.
The results suggest...
