Acm1 contributes to nuclear positioning by inhibiting Cdh1-substrate interactions.

Area of Science:

• Cell biology
• Molecular biology
• Genetics

Background:

• The anaphase-promoting complex (APC) is a crucial regulator of cell division, controlled by coactivators like Cdh1 and Cdc20.
• Pseudosubstrate binding is a known mechanism for regulating APC activity.
• The biological role of budding yeast Acm1, a Cdh1 pseudosubstrate inhibitor, remained undetermined.

Purpose of the Study:

• To elucidate the function of the budding yeast protein Acm1.
• To investigate the mechanism by which Acm1 regulates the APC/Cdh1 complex.
• To identify the specific Cdh1 substrates involved in the Acm1-mediated regulatory pathway.

Main Methods:

• Gene deletion studies in budding yeast to create Acm1-deficient cells.
• Analysis of nuclear positioning and spindle morphology during mitosis.
• Biochemical assays to assess Cdh1 substrate stability.
• Functional analysis of Cdh1 mutants with altered substrate binding capabilities.

Main Results:

• Acm1-deficient cells display significant defects in nuclear positioning and spindle morphology during mitosis.
• Loss of Acm1 does not lead to the destabilization of Cdh1 substrates.
• Expression of Cdh1 mutants that bind substrates but are catalytically inactive phenocopies the acm1 deletion phenotype.
• The bud neck-localized kinase Hsl1 is implicated as a key substrate affected in Acm1-deficient cells.

Conclusions:

• Acm1's primary role is not to inhibit APC/Cdh1 enzymatic activity but to prevent premature interactions between Cdh1 and its substrates.
• Regulation of coactivator-substrate interactions is essential for proper cell division.
• The findings suggest that pseudosubstrate-mediated regulation of APC/Cdh1 is a conserved mechanism across eukaryotes.