Fig. 8. The actin phenotypes of sla1sla2 cells. (A) Sensitivity to the actin monomer binding drug LAT-A is proposed to reflect the level of actin monomer in cells and therefore can be used to assess to whether a protein increases or decreases the stability of F-actin. Sensitivity to LAT-A was assessed by halo assay as described in Materials and Methods. These results are summarised graphically. Deletion of sla1 reduces the sensitivity to LAT-A whereas sla2 cells are more sensitive to the effects of the drug. The double mutant strains displayed an intermediate phenotype. The data shown are the average of three halo assays. Strains tested were KAY302, KAY97, KAY136 and KAY128. (B) Rhodamine-phalloidin was used to stain the F-actin of wild-type (KAY302), sla1 (KAY97), sla2 (KAY136) and sla1sla2 (KAY128) cells. In the absence of both sla1p and Sla2p, actin is largely localised to the distal pole of the cell. However, in these cells small, less bright patches could often be seen at polarised regions of the cell (arrows), and actin was also seen at the cytokinetic ring (arrowheads) but this represented a small fraction of the actin that was visualised. Bar, 10 µm. To ascertain whether this larger aggregation of actin patches was likely to be functional, the localisation of two F-actin-binding proteins was determined. Both Sac6p (C) and Abp1p (D) were also observed to localise to the distal regions of the cell, indicating that the actin in these structures is associated with a normal complement of actin-binding proteins. Bar, 10 µm.

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