Identification of cold-sensitive mutations in the Schizosaccharomyces pombe actin locus

In recent years, the actin cytoskeleton in Schizosaccharomyces pombe has be come the subject of intense scrutiny, However, to date, only a single actin mutation has been identified, Described here is the isolation and characte rization of four new cold-sensitive actin mutations. Sequence analysis of t he mutant actin genes indicated that each of these mutations caused alterat ions in single amino acids that are conserved in all actin sequences. These mutants differ in their phenotypes, One of these mutations (act1-48) was i dentified as an extragenic suppressor of a mutation in the cdc4 gene, which is required for actin ring formation and cytokinesis. Interestingly, when act1-48 mutant cells were shifted to the restrictive temperature, actin pat ches were not detected but the actin ring formation and stability was unaff ected. The three other mutations, act1-16, act1-32 and act1-67, primarily a ffected the actin ring formation or stability while F-actin patches did not seem to be substantially different in appearance. Given that the ultrastru ctural architectures of F-actin patches and the F-actin ring are presently unclear, these mutations, which affect one structure or the other, should b e useful for future studies on the role of actin itself in the function of these F-actin-containing structures in S. pombe. (C) 1999 Federation of Eur opean Biochemical Societies.