A number of proteins make up the Cdc28 complex in Saccharomyces cerevisiae, and regulate CDK activity. The cell cycle regulator Nik1 (Hsl1) is a protein kinase that interacts with the Cdc28 complex. The growth inhibitor Gin4 is structurally similar to Nik1 and may play a redundant role in the regulation of the cell cycle. We investigated the functions of Gin4 with respect to those of Nik1.
GIN4 was not essential for growth, and cells deficient in the GIN4 gene displayed no obvious defects in cell cycle regulation. The Δgin4 Δnik1 strain was temperature sensitive and showed an abnormal cell shape and FACS profile at permissive temperatures. GFP-fused Gin4 was localized at the bud-neck from late G1 to the M phase. Overproduction of the C-terminal portion of Gin4 was toxic for cell growth, and this domain was required for the bud-neck localization of Gin4-GFP. High copy expression of Gin4-GFP disturbed the bud-neck localization of Gin4 in the abnormally elongated cells. Cytokinesis was defective in the Δgin4 cdc28 double mutants. The GST-Gin4 fusion protein physically associates with the Cdc28 complex.
Gin4 is a bud-neck protein. GIN4 and NIK1 have distinct but partially overlapping functions. The major function of GIN4 is to ensure proper mitotic progression and cytokinesis.