Related Experiment Video

Updated: Aug 7, 2026

Cycloheximide Chase Analysis of Protein Degradation in Saccharomyces cerevisiae
09:05

Cycloheximide Chase Analysis of Protein Degradation in Saccharomyces cerevisiae

Published on: April 18, 2016

Saccharomyces cerevisiae Ime2 phosphorylates Sic1 at multiple PXS/T sites but is insufficient to trigger Sic1

Chantelle Sedgwick1, Matthew Rawluk, James Decesare

  • 1Department of Biochemistry, 561 Medical Sciences Building, University of Alberta, Edmonton, AB, T6G 2H7, Canada.

The Biochemical Journal
|June 17, 2006
PubMed

Insights

During yeast sporulation, the destruction of Sic1, a key inhibitor of DNA replication, is essential. While Ime2 kinase phosphorylates Sic1, it is not sufficient alone for its degradation, highlighting a complex regulatory mechanism.

Area of Science:

  • Cell Cycle Regulation
  • Molecular Biology
  • Yeast Genetics

Background:

  • DNA replication initiation in Saccharomyces cerevisiae requires Sic1 destruction.
  • In proliferating cells, Cln-Cdc28 complexes target Sic1 for degradation via SCF(Cdc4) and the proteasome.
  • During sporulation, Sic1 is degraded at the G1-/S boundary despite the absence of cyclins.

Purpose of the Study:

  • To investigate the mechanism of Sic1 destruction during yeast sporulation.
  • To determine the role of the meiosis-specific kinase Ime2 in Sic1 degradation.
  • To identify phosphorylation sites and regulatory motifs for Ime2.

Main Methods:

  • In vitro phosphorylation assays using Ime2 and Sic1.
  • Analysis of Sic1 phosphorylation sites and their correspondence to Cdk sites.
  • Ubiquitination assays in sporulating cells.
  • Expression studies of Ime2 in G1-arrested cells.

Main Results:

  • Sic1 destruction during sporulation requires Cdk phosphorylation sites.
  • Sic1 is ubiquitinated in sporulating cells, dependent on SCF(Cdc4).
  • Ime2 phosphorylates Sic1 at multiple sites in vitro, defining a PXS/T motif.
  • Ime2-phosphorylated Sic1 does not bind SCF(Cdc4), and Ime2 expression alone does not induce Sic1 destruction.

Conclusions:

  • Ime2 is necessary but not sufficient for Sic1 destruction during sporulation.
  • A model is proposed where Ime2 phosphorylation primes Sic1, but additional factors are required for SCF(Cdc4) binding and degradation.

More Related Videos

Growth-based Determination and Biochemical Confirmation of Genetic Requirements for Protein Degradation in Saccharomyces cerevisiae10:57

Growth-based Determination and Biochemical Confirmation of Genetic Requirements for Protein Degradation in Saccharomyces cerevisiae

Published on: February 16, 2015

Saccharomyces cerevisiae Models of Alzheimer's Disease to Screen Genes, Mutations, and Chemicals Affecting Amyloid Beta Production by γ-Secretase11:57

Saccharomyces cerevisiae Models of Alzheimer's Disease to Screen Genes, Mutations, and Chemicals Affecting Amyloid Beta Production by γ-Secretase

Published on: June 24, 2025

Related Concept Videos

Separation of Sister Chromatids02:17

Separation of Sister Chromatids

At the transition from prophase to metaphase, there is a reduction in cohesion along the chromosomal arms, resulting in the resolution of sister chromatids. However, residual cohesin connections remain to hold the sister chromatids together until the transition from metaphase to anaphase. The residual connection prevents any premature separation of sister chromatids, blocking the risks of aneuploidy within the daughter cells.
At the onset of anaphase, separase, a proteolytic enzyme, is...
Meiosis II02:02

Meiosis II

Meiosis II entails cell division and segregation of the sister chromatids, resulting in the production of four unique haploid gametes. The steps for meiosis II are similar to mitosis, except that meiosis II occurs in haploid cells, whereas mitosis occurs in diploid cells.
The timing and cell division patterns of meiosis differ between males and females. In male meiosis, the centrosomes are part of the formation of the meiotic spindle. However, in oocytes, including that of humans, Drosophila,...
Anaphase Promoting Complex00:50

Anaphase Promoting Complex

The stepwise destruction of specific proteins is necessary for the progression and completion of the cell cycle. Such proteins are ubiquitinated by ubiquitin ligases and then subsequently destroyed by the proteasome. The SCF (Skp1/Cullin/F-box) and the anaphase-promoting complex (APC) are two important ubiquitin ligases involved in cell cycle progression. While SCF is active throughout the cell cycle, APC gets activated during metaphase to anaphase transition. Cdc20 or Cdh1 binds to APC and...
The Spindle Assembly Checkpoint02:19

The Spindle Assembly Checkpoint

The spindle assembly checkpoint is a molecular surveillance mechanism ensuring the fidelity of chromosome segregation during anaphase. The checkpoint monitors the completion of all the prerequisite steps before chromosome segregation to determine whether the segregation process should proceed or be delayed.
Many proteins function together to control the spindle assembly checkpoint. Mutations affecting these proteins may allow cells to proceed into anaphase prematurely, resulting in the...
Inhibition of Cdk Activity02:34

Inhibition of Cdk Activity

The orderly progression of the cell cycle depends on the activation of Cdk protein by binding to its cyclin partner. However, the cell cycle must be restricted when undergoing abnormal changes. Most cancers correlate to the deregulated cell cycle, and since Cdks are a central component of the cell cycle, Cdk inhibitors are extensively studied to develop anticancer agents. For instance, cyclin D associates with several Cdks, such as Cdk 4/6, to form an active complex. The cyclin D-Cdk4/6 complex...