 Solution

Disrupting the dynamic actin network compromises processes required for sustained proliferation: endocytosis, directed delivery of cell membrane and cell-wall material, maintenance of polarized cell growth and successful cytokinesis. Failure of these actin-dependent functions can cause growth arrest and, under sufficiently damaging conditions, loss of viability. The altered sensitivity of actin mutants supports an actin-related mechanism, with their different assembly properties potentially changing the reserve of functional cytoskeleton.

A clear zone itself establishes failure to form a visible lawn, not necessarily death. biological cells might remain viable but fail to bud or divide while drug is present. Recovery after drug removal and subsequent colony formation would distinguish reversible arrest from killing. The experiment also does not identify which actin-dependent process first becomes limiting; matched measurements of trafficking, budding and division would be needed for that ordering.