STRUCTURAL REARRANGEMENT OF THE ACTIN CYTOSKELETON IN REGENERATING PROTOPLASTS OF BUDDING YEASTS

In Saccharomyces cerevisiae cells the actin cytoskeleton is present as actin dots in the bud and around the septum, i.e. in areas of intensive cell wall synthesis, and as actin cables, which are loose bundles along the longitudinal cell axis. However, the apparently asymmetrical pattern of actin no longer persisted after protoplasting, when the cables disappeared and dots were evenly distributed under the whole protoplast surface. This pattern was maintained during regeneration of a new cell wall all over the protoplast surface, thus providing evidence of a relationship between the new wall formation and the presence of a regular arrangement of actin dots. The completed cell wall allowed the protoplast to bud and produce a normal daughter cell. However, before the walled protoplast began to bud, actin dots accumulated at the site of bud emergence and actin cables appeared, extending to the cytoplasm. Later, actin dots accumulated in the growing bud, forming a ring in the neck, and actin cables passed to the bud. Completion of the protoplast-to-cell reversion was preceded by restoration of the normal actin cytoskeleton.