The two Physarum polycephalum profilins are not functionally equivalent inyeast cells

Profilin is a ubiquitous actin-monomer-binding protein. The protist Physaru m polycephalum contains two profilins, ProA and ProP, present in amoebae an d plasmodia, respectively. We have used mutant Saccharomyces cerevisiae cel ls in an attempt to observe distinct functions for the two profilins. Profi lin-deficient yeast cells (Delta pfy1) have delocalized actin cortical patc hes, do not contain visible actin cables, have reduced mating efficiency an d do not grow at 37 degrees C or in the presence of caffeine. Deletion of t he SRV2 gene (Delta srv2), coding for the adenylyl cyclase-associated prote in, also results in an altered actin distribution and an inability to survi ve on rich medium. We found that the Delta pfy1 and Delta srv2 mutant pheno types were corrected equally well by the overexpression of Physarum ProA or yeast Pfy1p profilins. The Delta pfy1 cells overexpressing ProP have impro ved mating efficiency and a normal distribution of actin cortical patches. These cells however, have barely detectable actin cables, do not grow at 37 degrees C, and are sensitive to caffeine. Also, the expression of ProP doe s not correct the growth defect of the Delta srv2 cells. These results sugg est that the two Physarum proteins are not functionally equivalent in yeast cells. No difference was detected in the affinity of ProA and ProP for pol y-L-proline, while ProA has a slightly greater affinity than ProP for phosp hatidylinositol 4,5-biphosphate.