The Nim1-kinase Gin4 has distinct domains crucial for septin assembly, phospholipid binding, and mitotic exit

Jie Ying Au Yong,Yan-Ming Wang,Yue Wang

doi:10.1242/jcs.183160

Abstract

ABSTRACTIn fungi, the Nim1 protein kinases, such as Gin4, are important regulators of multiple cell cycle events, including the G2–M transition, septin assembly, polarized growth and cytokinesis. Compelling evidence has linked some key functions of Gin4 with the large C-terminal non-kinase region which, however, is poorly defined. By systematically dissecting and functionally characterizing the non-kinase region of Gin4 in the human fungal pathogen Candida albicans, we report the identification of three new domains with distinct functions: a lipid-binding domain (LBD), a septin-binding domain (SBD) and a nucleolus-associating domain (NAD). The LBD and SBD are indispensable for the function of Gin4, and they alone could sufficiently restore septin ring assembly in GIN4-null mutants. The NAD localizes to the periphery of the nucleolus and physically associates with Cdc14, the ultimate effector of the mitotic exit network. Gin4 mutants that lack the NAD are defective in spindle orientation and exit mitosis prematurely. Furthermore, we show that Gin4 is a substrate of Cdc14. These findings provide novel insights into the roles and mechanisms of Nim1 kinases in the regulation of some crucial cell cycle events.

Highlights

Cell division requires temporal precision in the sequential coordination of events that are monitored and enforced through surveillance mechanisms called checkpoints (Hartwell and Weinert, 1989; Lew and Burke, 2003; Murray, 1992; Rudner and Murray, 1996; Zhou and Elledge, 2000)
Under GIN4-OFF conditions, the gin4CT1Δ cells exhibited morphological defects similar to the gin4Δ/Δ cells in which no septin ring was formed, and GFP–Gin4CT1Δ colocalized with Cdc12–mCherry to pseudohyphal tips (Fig. 1B, bottom), indicating that gin4CT1Δ cannot support septin ring formation and that CT1 is essential for Gin4 function
The ability of Gin4CT1Δ to colocalize with the septins both at the bud neck in GIN4 expression (GIN4-ON) cells and at the pseudohyphal tips in GIN4-OFF cells suggests that CT1 is not required for Gin4 to associate with septin complexes

Summary

Introduction

Cell division requires temporal precision in the sequential coordination of events that are monitored and enforced through surveillance mechanisms called checkpoints (Hartwell and Weinert, 1989; Lew and Burke, 2003; Murray, 1992; Rudner and Murray, 1996; Zhou and Elledge, 2000). In Schizosaccharomyces pombe, the Nim kinases Cdr and Cdr are essential components of the cell size checkpoint, which promote the G2–M transition by downregulating the CDK inhibitor Wee (Kanoh and Russell, 1998; Moseley et al, 2009). In Saccharomyces cerevisiae (Sc), a homologous kinase Hsl plays a similar role in the morphogenesis checkpoint

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Conclusion