A GTPase that goes both ways

Cellular GTPases are generally placed into one of two categories: signaling switches such as the oncogene ras or assembly factors such as the translation elongation factor EF-Tu (EF-1a in eukaryotes). But on page 315, Gladfelter et al. show that yeast Cdc42p, a well-characterized ras-like switch, can also behave as an EF-Tu–like assembly factor. The work is the first description of a GTPase changing hats in this way, and it suggests that GTPases may defy strict categorization.Like all ras-like GTPases, Cdc42p activates downstream effectors when bound to GTP, and stops signaling after it hydrolyzes the GTP to GDP. In an effort to study Cdc42p activity during the assembly of the septin ring, a structure important in yeast budding, the authors characterized two cdc42 mutants with defects in septin...