INDUCTION OF F-ACTIN RINGS IN REGENERATING PROTOPLASTS OF THE CDC16 MUTANT SCHIZOSACCHAROMYCES-POMBE

Formation of continuous F-actin rings was induced in regenerating prot oplasts of the temperature-sensitive mutant of Schizosaccharomyces pom be defective in cdc]6 gene. The proportion of ring-containing protopla sts freshly prepared from cdc16 mutant cells exponentially growing at permissive temperature (10%) corresponded to the proportion of mitotic cells in the starting culture. This suggests that the actin rings sur vived protoplast formation as was found in the wild type strain of S. pombe (Jochova et al. 1991). In 87% of the cdc16 mutant protoplasts pr epared under permissive conditions and then cultivated at 37-degrees-C in the absence of digesting enzyme, F-actin bundle assembly was initi ated within 3 h. F-actin formed either abundant cables (in 63% of thes e spheroplasts) or distinct continuous rings (in 37% of the spheroplas ts). In some spheroplasts two rings or partially split single rings we re formed. These results indicate that F-actin rings not only persist during protoplast formation but also can be induced when the protoplas ts are further cultivated under reversion conditions.