Three actin cross-linking proteins, the 34 kDa actin-bundling protein, alpha-actinin and gelation factor (ABP-120), have both unique and redundant roles in the growth and development of Dictyostelium

The contribution of three actin cross-linking proteins, alpha-actinin (alph a A), gelation factor (ABP-120), and the 34 kDa actin-bundling protein to c ellular functions has been studied in three single mutant (alpha A(-), 120( -), and 34(-)) and three double mutant (alpha A(-)/120(-), 34(-)/alpha A(-) , 34(-)/120(-)) strains of Dictyostelium generated by homologous recombinat ion, Strains alpha A-/120- and 34(-)/alpha A(-) exhibited a reduced rate of pinocytosis, grew to lower saturation densities, and produced small cells in shaking cultures. All strains grew normally in bacterial suspensions and on agar plates with a bacterial lawn. Slow growth under conditions of redu ced temperature and increased osmolarity was observed in single mutants 34( -) and alpha A(-), respectively, as well as in some of the double mutant st rains. Motility, chemotaxis, and development were largely unaltered in 34(- )/alpha A(-) and 34-/120- cells. However, 34(-)/alpha A(-) cells showed enh anced aggregation when starved in suspension. Moreover, morphogenesis was i mpaired in both double mutant strains and fruiting bodies of aberrant morph ology were observed. These defects were reverted by re-expression of one of the lacking crosslinking proteins. The additive and synthetic phenotypes o f these mutations indicate that actin cross-linking proteins serve both uni que and overlapping functions in the actin cytoskeleton.