The exozymocin secreted by Kluyveromyces lactis causes sensitive yeast cells, including Saccharomyces cerevisiae, to arrest growth in the G(1) phase of the cell cycle. Despite its heterotrimeric (alphabetagamma) structure, intracellular expression of its smallest subunit, the gamma-toxin, is alone responsible for the G(1) arrest. The alpha subunit, however, has a chitinase activity that is essential for holozymocin action from the cell exterior. Here we show that sensitive yeast cells can be rescued from zymocin treatment by exogenously applying crude chitin preparations, supporting the idea that chitin polymers can compete for binding to zymocin with chitin present on the surface of sensitive yeast cells. Consistent with this, holozymocin can be purified by way of affinity chromatography using an immobilized chitin matrix. PCR-mediated deletions of chitin synthesis (CHS) genes show that most, if not all, genetic scenarios that lead to complete loss (chs3Delta), blocked export (chs7Delta) or reduced activation (chs4Delta), combined with mislocalization (chs4Deltachs5Delta; chs4Deltachs6Delta; chs4Deltachs5Deltachs6Delta) of chitin synthase III activity (CSIII), render cells refractory to the inhibitory effects of exozymocin. In contrast, deletions in CHS1 and CHS2, which code for CSI and CSII, respectively, have no effect on zymocin sensitivity. Thus, CSIII-polymerized chitin, which amounts to almost 90% of the cell's chitin resources, appears to be the carbohydrate receptor required for the initial interaction of zymocin with sensitive cells.CI - Copyright 2001 John Wiley & Sons, Ltd.
|Evidence ID||Analyze ID||Interactor||Interactor Systematic Name||Interactor||Interactor Systematic Name||Type||Assay||Annotation||Action||Modification||Phenotype||Source||Reference||Note|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Gene Ontology Term||Gene Ontology Term ID||Qualifier||Aspect||Method||Evidence||Source||Assigned On||Reference||Annotation Extension|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Phenotype||Experiment Type||Experiment Type Category||Mutant Information||Strain Background||Chemical||Details||Reference|
|Evidence ID||Analyze ID||Regulator||Regulator Systematic Name||Target||Target Systematic Name||Experiment||Conditions||Strain||Source||Reference|