Fig. 7. Summary and Model. (A) Summary of cellular behavior in differing genotypes and growth conditions. Actin patches and rings are shown in red. Nuclei are shown as black circles. Cdc7p localization to the spindle pole body (a marker of active SIN) is shown schematically as a blue circle. Wild-type or clp1 cells under normal growth conditions (column 1); wild-type or clp1 cells upon treatment with low doses of Lat A (columns 2 and 3, respectively); cps1-191 and clp1 cps1-191 cells at the restrictive temperature of 36°C (columns 4 and 5, respectively); a SIN mutant at the restrictive temperature of 36°C (column 6). (B) Model. Upon perturbation of the cytokinesis machinery Clp1p and the SIN function in a positive feedback loop to maintain the integrity of the actomyosin ring (see Discussion).