The twoPhysarum polycephalum profiling are not functionally equivalent in yeast cells

Summary Profilin is a ubiquitous actin-monomer-binding protein. The protistPhysarum polycephalum contains two profilins, ProA and ProP, present in amoebae and plasmodia, respectively. We have used mutantSaccharomyces cerevisiae cells in an attempt to observe distinct functions for the two profilins. Profilin-deficient yeast cells (pfy1) have delocalized actin cortical patches, do not contain visible actin cables, have reduced mating efficiency and do not grow at 37 °C or in the presence of caffeine. Deletion of theSRV2 gene (srv2), coding for the adenylyl cyclase-associated protein, also results in an altered actin distribution and an inability to survive on rich medium. We found that the pfy1 and srv2 mutant phenotypes were corrected equally well by the overexpression of Physarum ProA or yeast Pfy1p profilins. The pfy1 cells overexpressing ProP have improved mating efficiency and a normal distribution of actin cortical patches. These cells, however, have barely detectable actin cables, do not grow at 37 °C, and are sensitive to caffeine. Also, the expression of ProP does not correct the growth defect of the srv2 cells. These results suggest that the two Physarum proteins are not functionally equivalent in yeast cells. No difference was detected in the affinity of ProA and ProP for poly-L-proline, while ProA has a slightly greater affinity than ProP for phosphatidylinositol 4,5-biphosphate.Abbreviations FITC tfluorescein isothiocyanate - PIP₂ phosphatidylinositol 4,5-biphosphate - YPD yeast extract peptone dextrose