Cell integrity and morphogenesis in a budding yeast septin mutant

Abstract

The non-sporulating diploid strain V327 of Saccharomyces cerevisiae was previously isolated in a search for thermosensitive autolytic mutants. This strain is very efficient a t releasing intracellular proteins into the medium when incubated a t high temperatures. The expression of this lytic phenotype depends on a morphogenetic defect, consisting of the appearance of elongated chains of cells. Transmission electron microscopy revealed a mislocalization of septa at semi-permissive temperatures and a total lack of septation together with abnormal cell wall architecture a t a non-permissive temperature. The septin-encoding CDClO gene was cloned by complementation of the pleiotropic phenotype of the V327 mutant. Rescue and sequencing of CDClO alleles from V327 revealed a point mutation that created a single amino acid change in a region which is well conserved among septins. This new allele was named cdcl0-77. The construction of a cdcl0-ll haploid strain by substituting the CDClO gene with the rescued allele permitted further genetic analyses of the mutation and allowed the construction of new homozygous cdcl0-ll diploid strains that showed a reduced ability to sporulate. Fusing both the wild-type and the cdcl0-ll alleles to green fluorescent protein (GFP) demonstrated that the mutation does not affect the localization of this septin to the bud neck a t the standard growth temperature of 24 OC, although the morphogenetic phenotype a t 37 OC parallels the disappearance of CdclO-GFP a t the ring encircling the septum area.1

Highly Dynamic and Specific Phosphatidylinositol 4,5-Bisphosphate, Septin, and Cell Wall Integrity Pathway Responses Correlate with Caspofungin Activity against Candida albicans

“…The septation defects observed in the present study are also similar to those seen in S. cerevisiae mutants with mislocalized septins (14,(44)(45)(46). The S. cerevisiae septation apparatus, which includes septins and chitin synthase, can function autonomously at ectopic locations independently of cell division (14).…”

Kinetic partitioning during de novo septin filament assembly creates a critical G1 “window of opportunity” for mutant septin function

“…39 We have previously discussed possible examples for distinct alleles/isoforms of a and b tubulins. 15 Additionally, a recent study investigating "assembly control" exerted by chaperones resident in the ER on the ab heterodimer of the T cell receptor (TCR) concluded that folding of the a and b subunits is dimerization-dependent, leading chaperones to sequester nascent a and b polypeptides until they have achieved native folds in the context of the ab heterodimer, which is linked irreversibly together by disulfide bonds.…”

The yeast endocytic protein Epsin 2 functions in a cell-division signaling pathway

“…In fact, septin mutant cells have strikingly similar phenotypes to those induced by ENTH2 overexpression (Fig. 1B-D), including chains of cells with aberrant septum formation (Versele and Thorner, 2004;Schmidt et al, 2003;Roh et al, 2002;Cid et al, 1998). Therefore, we asked whether septin assembly is affected by the ENTH2-specific dominant-negative effect.…”

“…Interestingly, some of these mutants have been reported to interact poorly with the septin-organizing protein Bem3 (Richman and Johnson, 2000). Furthermore, septin deficiencies produced phenotypes very similar to those observed upon ENTH2 overexpression, including elongated, chained buds and aberrant septa (Versele and Thorner, 2004;Schmidt et al, 2003;Roh et al, 2002;Cid et al, 1998).…”