Fig. 1. Stability of centrosomal proteins following inhibition of Hsp90 and heat shock. Cell extracts obtained from Drosophila SL2 cells treated with the Hsp90 inhibitor geldanamycin (A) or heat shock (B) were prepared at different time points, run in SDS–PAGE gels and blotted with antibodies against a panel of centrosomal proteins. Of 15 centrosomal proteins examined, Polo was destabilized following geldanamycin treatment, Hsp90, Hsp70 and Cnn increased slightly and the rest of the proteins did not change. Heat shock, which also leads to an increase in Hsp90, does not have any noticeable effect on the levels of Polo (B). Immunoprecipitated Polo from heat shocked cells maintains kinase activity (C). Heat shock-induced centrosome dispersion can be observed as early as 1 h (D). The centrosomal marker CP190, microtubules and DNA are shown in red, green and blue. The spindle poles are labelled with arrowheads.