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Septins, under Cla4p regulation, and the chitin ring are required for neck integrity in budding yeast
Martin Schmidt1, Archana Varma, Tomás Drgon
1National Institute of Diabetes and Digestive and Kidney Diseases, Laboratory of Biochemistry and Genetics, Bethesda, Maryland 20892, USA.
Abstract:
CLA4, encoding a protein kinase of the PAK type, and CDC11, encoding a septin, were isolated in a screen for synthetic lethality with CHS3, which encodes the chitin synthase III catalytic moiety. Although Ste20p shares some essential function with Cla4p, it did not show synthetic lethality with Chs3p. cla4 and cdc11 mutants exhibited similar morphological and septin localization defects, including aberrant and ectopic septa. Myo1p, which requires septins for localization, formed abnormally wide rings in cla4 mutants. In cultures started with unbudded cells, an inhibitor of Chs3p activity, nikkomycin Z, aggravated the abnormalities of cla4 and cdc11 mutants and gave rise to enlarged necks at the mother-bud junction, leading to cell death. It is concluded that Cla4p is required for the correct localization and/or assembly of the septin ring and that both the septin ring and the Chs3p-requiring chitin ring at the mother-bud neck cooperate in maintaining the neck constricted throughout the cell cycle, a vital function in budding yeast.
Insights
The protein kinase Cla4p and septin Cdc11p are essential for proper cell division in budding yeast. They cooperate with chitin synthase III to maintain neck constriction, preventing cell death.
Area of Science:
- Cell biology
- Molecular genetics
- Biochemistry
Background:
- Chitin synthase III (Chs3p) is crucial for cell wall synthesis in budding yeast.
- Septins, like Cdc11p, form rings at the mother-bud neck and are involved in cytokinesis.
- PAK-type kinases, such as Cla4p, play roles in cell cycle regulation and morphogenesis.
Purpose of the Study:
- To investigate the genetic interactions between CHS3, CLA4, and CDC11.
- To elucidate the roles of Cla4p and Cdc11p in relation to Chs3p function during budding yeast cell division.
Main Methods:
- Synthetic lethality screening to identify genes interacting with CHS3.
- Analysis of morphological and protein localization defects in yeast mutants.
- Treatment with nikkomycin Z, a Chs3p inhibitor, to assess combined effects.
Main Results:
- Synthetic lethality was observed between cla4 and cdc11 mutants with CHS3.
- cla4 and cdc11 mutants displayed defects in septin localization and aberrant septa formation.
- Inhibition of Chs3p activity exacerbated these defects, leading to cell death.
Conclusions:
- Cla4p is essential for the correct localization and assembly of the septin ring.
- The septin ring and the chitin ring at the mother-bud neck cooperate to maintain neck constriction.
- This cooperation is vital for cell cycle progression and survival in budding yeast.