The Saccharomyces cerevisiae SDA1 gene is required for actin cytoskeleton organization and cell cycle progression

The organization of the actin cytoskeleton is essential for several cellular processes. Here we report the characterization of a Saccharomyces cerevisiae novel gene, SDA1, encoding a highly conserved protein, which is essential for cell viability and is localized in the nucleus. Depletion or inactivation of Sda1 cause cell cycle arrest in G 1 by blocking both budding and DNA replication, without loss of viability. Furthermore, sda1-1 temperature-sensitive mutant cells arrest at the non-permissive temperature mostly without detectable structures of polymerized actin, although a normal actin protein level is maintained, indicating that Sda1 is required for proper organization of the actin cytoskeleton. To our knowledge, this is the first mutation shown to cause such a phenotype. Recovery of Sda1 activity restores proper assembly of actin structures, as well as budding and DNA replication. Furthermore we show that direct actin perturbation, either in sda1-1 or in cdc28-13 cells released from G 1 block, prevents recovery of budding and DNA replication. We also show that the block in G 1 caused by loss of Sda1 function is independent of Swe1. Altogether our results suggest that disruption of F-actin structure can block cell cycle progression in G 1 and that Sda1 is involved in the control of the actin cytoskeleton.