High levels of profilin suppress the lethality caused by overproduction of actin in yeast cells.

Overproduction of actin is lethal to yeast cells. In contrast, overexpression of the profilin gene, PFY1, encoding an actin-binding protein, leads to no very obvious phenotype. Interestingly, profilin overproduction can compensate for the deleterious effects of too much actin in a profilin concentration-dependent manner. Our results, thus, document that actin and profilin interact in vivo. Immunofluorescence studies suggest that suppression works by reducing actin assembly. We observed, however, that even massive overproduction of profilin fails to fully restore the wild-type phenotype (e.g. the wild-type appearance of the actin microfilament system). This may indicate that actin monomer sequestration is not the only mechanism by which the balance of actin polymerization is controlled.