The integrity of the fungal cell wall is ensured by a signal transduction pathway, the so-called CWI pathway, which has best been studied in the model yeast Saccharomyces cerevisiae. In this context, environmental stress and other perturbations at the cell surface are detected by a small set of plasma membrane-spanning sensors, viz. Wsc1, Wsc2, Wsc3, Mid2 and Mtl1. This review covers the recent advances in sensor structure, sensor mechanics, their cellular distribution and their in vivo functions, obtained from genetic, biochemical, cell biological and biophysical investigations.

The glyoxylate cycle is essential for the utilization of C2 compounds by the yeast Saccharomyces cerevisiae. Within this cycle, isocitrate lyase catalyzes one of the key reactions. We obtained mutants lacking detectable isocitrate lyase activity, screening for their inability to grow on ethanol. Genetic and biochemical analysis suggested that they carried a defect in the structural gene, ICL1. The mutants were used for the isolation of this gene and it was located on a 3.1‐kb Bg/II‐SphI DNA fragment. We then constructed a deletion‐substitution mutant in the haploid yeast genome. It did not have any isocitrate lyase activity and lacked the ability to grow on ethanol as the sole carbon source. Both strands of a DNA fragment carrying the gene and its flanking regions were sequenced. An open reading frame of 1671 bp was detected, encoding a protein of 557 amino acids with a calculated molecular mass of 62515 Da. The deduced amino acid sequence shows extensive similarities to genes encoding isocitrate lyases from various organisms. Two putative cAMP‐dependent protein‐kinase phosphorylation sites may explain the susceptibility of the enzyme to carbon catabolite inactivation.

Cytokinesis in yeast can be achieved by plasma membrane ingression, which is dependent on actomyosin ring constriction. Inn1 presumably couples these processes by interaction with both the plasma membrane and the temporary actomyosin ring component Hof1. In addition, an actomyosin ring independent cytokinesis pathway exists in yeast. We here identified Cyk3, a key component of the alternative pathway, as a novel interaction partner of Inn1. The carboxy-terminal proline rich part of Inn1 binds the SH3 domains of either Cyk3 or Hof1. Strains with truncated proteins lacking either of these SH3 domains do not display any severe phenotypes, but are synthetically lethal, demonstrating their crucial role in cytokinesis. Overexpression of CYK3 leads to an actomyosin ring independent recruitment of Inn1 to the bud neck, further supporting the significance of this interaction in vivo. Moreover, overexpression of CYK3 in a myo1 or an iqg1 deletion not only restores viability, but also the recruitment of Inn1 to the bud neck. We propose that Cyk3 is part of an actomyosin ring independent cytokinesis pathway, which acts as a rescue mechanism to recruit Inn1 to the bud neck.

Human protein kinase C (PKC) isoforms have been implicated in diseases such as Alzheimer's, diabetes and cancers. In contrast to mammals, which have at least nine genes, fungi have only one or two. The yeast Saccharomyces cerevisiae produces only a single Pkc1 and is employed in the study of specific human isozymes, including their susceptibility to pharmacological drugs. Vice versa, the domain structure and regulation of yeast and other fungal PKCs yield insights into the function of human isozymes. Therefore, human PKCs are briefly reviewed herein and related to the yeast enzyme. The latter was originally implicated in the regulation of cell wall synthesis through a conserved MAP kinase pathway, but many more targets have now been described in S. cerevisiae and other fungi. These implicate PKC in the control of such diverse processes as the organization of the actin cytoskeleton, autophagy and apoptosis, nutrient sensing and ribosome biogenesis, cell cycle control, cytokinesis and genetic stability. PKC is a promising target for the development of antifungal drugs against pathogenic fungi such as Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus. Thus, fungal PKCs are drawing increased attention and the accumulating literature on the enzymes from different species is summarized herein.