Further characterization of the actin-related protein Act3p/Arp4 of S. cerevisiae through mutational analysis.

In the course of functional analysis of the yeast ARP4 (ACT3) gene, we further characterized the role of its protein product Arp4p in the cell. We report that although it is localized in the nucleus, Arp4p performs its function independently of binding to DNA directly. The roles of the core actin structure (the ATP-binding pocket) and a putative Nuclear Localization Signal (NLS) of Arp4p were tested by targeted mutagenesis. The results suggest that under normal conditions, the ATPase activity and the NLS are dispensable for the essential function of this protein in the cell. Furthermore, the use of reporter genes confirmed that Arp4p could be involved in some general mechanism of transcriptional regulation.