HIRA, the human homologue of yeast Hir1p and Hir2p, is a novel cyclin-cdk2 substrate whose expression blocks S-phase

Related Experiment Video

Updated: Aug 11, 2026

Development of Inhibitors of Protein-protein Interactions through REPLACE: Application to the Design and Development Non-ATP Competitive CDK Inhibitors
10:33

Development of Inhibitors of Protein-protein Interactions through REPLACE: Application to the Design and Development Non-ATP Competitive CDK Inhibitors

Published on: October 26, 2015

C Hall1, D M Nelson, X Ye

  • 1Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.

Molecular and Cellular Biology
|March 10, 2001
PubMed

Insights

Human HIRA protein is a substrate of cyclin-dependent kinase 2 (CDK2) enzymes. This finding reveals a new role for HIRA in cell cycle regulation.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • Cyclin-dependent kinase 2 (CDK2) kinases regulate the cell cycle.
  • CDK2 substrates possess specific sequence motifs: a cyclin-binding RXL motif and phosphoacceptor sites.
  • Human HIRA is homologous to yeast proteins involved in histone gene regulation.

Purpose of the Study:

  • To identify novel substrates of cyclin-CDK2 kinases.
  • To investigate whether human HIRA is a substrate of cyclin-CDK2.

Main Methods:

  • Database search for proteins with RXL and phosphoacceptor motifs.
  • In vitro kinase assays using purified cyclin A/E-CDK2 and HIRA.
  • In vivo phosphorylation studies using Western blotting and CDK2 inhibitors.
  • Cellular localization studies and analysis of cell cycle progression upon HIRA expression.

Main Results:

  • Human HIRA contains the necessary motifs and binds/is phosphorylated by cyclin A/E-CDK2 in vitro.
  • HIRA is phosphorylated in vivo on consensus CDK2 sites, including threonine 555, which is directly phosphorylated by cyclin A-CDK2.
  • HIRA phosphorylation is cell cycle-dependent (S phase), blocked by p21(cip1), and occurs in the nucleus, consistent with cyclin-CDK2 activity.

Conclusions:

  • Human HIRA is a novel in vivo substrate of cyclin-CDK2 kinases.
  • HIRA phosphorylation by cyclin-CDK2 occurs in the nucleus during S phase.
  • Ectopic HIRA expression causes S-phase arrest, suggesting a role in cell cycle control.

More Related Videos

Studying Cell Cycle-regulated Gene Expression by Two Complementary Cell Synchronization Protocols12:02

Studying Cell Cycle-regulated Gene Expression by Two Complementary Cell Synchronization Protocols

Published on: June 6, 2017

Combining Mitotic Cell Synchronization and High Resolution Confocal Microscopy to Study the Role of Multifunctional Cell Cycle Proteins During Mitosis08:33

Combining Mitotic Cell Synchronization and High Resolution Confocal Microscopy to Study the Role of Multifunctional Cell Cycle Proteins During Mitosis

Published on: December 5, 2017

Related Concept Videos

Positive Regulator Molecules01:45

Positive Regulator Molecules

To consistently produce healthy cells, the cell cycle—the process that generates daughter cells—must be precisely regulated.
Positive Regulator Molecules02:39

Positive Regulator Molecules

Mitotic cell division results in daughter cells that exactly resemble the parent cell. However, errors in the DNA replication or distribution of genetic material may lead to genetic mutations that may be passed down to every new cell formed from the resulting abnormal cell. Propagation of such mutant cells is restricted through checkpoint mechanisms present at different stages of the cell cycle. These checkpoints involve regulator molecules that either promote or demote cell cycle events.
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...
M-Cdk Drives Transition Into Mitosis02:15

M-Cdk Drives Transition Into Mitosis

Checkpoints throughout the cell cycle serve as safeguards and gatekeepers, allowing the cell cycle to progress in favorable conditions and slow or halt it in problematic ones. This regulation is known as the cell cycle control system.
Cyclin-dependent kinases, or Cdks, work in concert with cyclins to control cell cycle transitions. M-Cdk, a complex of Cdk1 bound to M cyclin, is a well-known example of this coordinated control that drives the transition from the G2 to the M phase.
M cyclin...
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...
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...