The role of Saccharomyces cerevisiae coronin in the actin and microtubule cytoskeletons.

Coronin was originally identified as a cortical protein associated with the actin cytoskeleton in Dictyostelium [1]. More recent studies have revealed that coronin is involved in actin-based motility, cytokinesis and phagocytosis [2,3]. Here, we describe the identification of a single homolog of coronin in Saccharomyces cerevisiae, which we show localizes to cortical actin patches in an actin-dependent manner. Unlike Dictyostelium mutants that lack coronin, yeast strains lacking coronin had no detectable defects in actin-based processes. This may reflect differences in the functions of the actin cytoskeleton in these two organisms. Previous studies have shown that cortical actin may mediate astral microtubule-based movements of the mitotic spindle in S. cerevisiae [4,5] and that, during mitosis in Dictyostelium, the regions of the cell cortex that overlap with astral microtubules become enriched in actin and coronin [6]. We therefore examined whether yeast lacking coronin had defects in the microtubule cytoskeleton. The mutant strains had increased sensitivity to the microtubule-destabilizing drug benomyl and an increased number of large-budded cells with short spindles. Further examination of microtubule-related processes, including spindle formation, migration of the mitotic spindle to the bud neck, spindle elongation, and translocation of the elongating spindle through the bud neck, failed to reveal any defects in the coronin mutant. Taken together, these results suggest that S. cerevisiae coronin is a component of the actin cytoskeleton that may interact with the microtubule cytoskeleton.