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Studying Proteolysis of Cyclin B at the Single Cell Level in Whole Cell Populations
10:54

Studying Proteolysis of Cyclin B at the Single Cell Level in Whole Cell Populations

Published on: September 17, 2012

Human cyclin A is adenovirus E1A-associated protein p60 and behaves differently from cyclin B

J Pines1, T Hunter

  • 1Molecular Biology and Virology Laboratory, Salk Institute for Biological Studies, San Diego, California 92138.

Nature
|August 23, 1990
PubMed

Insights

Cyclins A and B are key cell cycle proteins. This study reveals cyclin A levels fluctuate during the cell cycle, preceding cyclin B, and associates with a distinct kinase.

Area of Science:

  • Cell biology
  • Molecular biology
  • Biochemistry

Background:

  • Cyclins are proteins crucial for cell cycle progression, synthesized and degraded cyclically.
  • Cyclins are linked to mitosis induction and form part of the mitosis promoting factor (MPF) with p34cdc2.
  • Cyclins are classified into A and B types based on conserved motifs.

Purpose of the Study:

  • To investigate the cell cycle regulation and binding partners of human cyclin A.
  • To compare the expression patterns of cyclin A and cyclin B during the cell cycle.
  • To characterize the enzymatic activity of cyclin A-associated complexes.

Main Methods:

  • Cloning of human cyclin A and B.
  • Analysis of cyclin A and B mRNA and protein levels throughout the cell cycle.
  • Biochemical assays to determine kinase activity of cyclin A complexes.
  • Immunoprecipitation to identify associated proteins.

Main Results:

  • Human cyclin A mRNA and protein levels exhibit cell cycle-dependent variations.
  • Cyclin A levels rise and fall before those of cyclin B during the cell cycle.
  • Cyclin A forms a complex with a 33 kDa protein distinct from p34cdc2, exhibiting histone H1 kinase activity.
  • Cyclin A is identified as p60, associating with p34cdc2 in interphase and adenovirus E1A in transformed cells.

Conclusions:

  • Cyclin A plays a distinct role in cell cycle progression, with its expression preceding cyclin B.
  • The cyclin A-p33 complex represents a novel kinase activity involved in cell cycle regulation.
  • Cyclin A's association with different partners (p34cdc2, adenovirus E1A) suggests diverse functions in normal and transformed cells.

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