Both cyclin A and cyclin E have S-phase promoting (SPF) activity in Xenopus egg extracts

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Reconstitution of Cell-cycle Oscillations in Microemulsions of Cell-free Xenopus Egg Extracts
06:31

Reconstitution of Cell-cycle Oscillations in Microemulsions of Cell-free Xenopus Egg Extracts

Published on: September 27, 2018

U P Strausfeld1, M Howell, P Descombes

  • 1Imperial Cancer Research Fund, Clare Hall Laboratories, Potters Bar, Herts, England.

Journal of Cell Science
|June 1, 1996
PubMed

Insights

Cyclin-dependent kinases (Cdks) drive DNA replication in Xenopus egg extracts. Cyclin E1-Cdk2 and Cyclin A-Cdc2 complexes provide essential S-phase promoting factor (SPF) activity for DNA synthesis.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Developmental Biology

Background:

  • Protein synthesis inhibition in Xenopus egg extracts permits one round of DNA replication.
  • Cyclin-dependent kinases (Cdks) are crucial regulators of the cell cycle.

Purpose of the Study:

  • To identify the specific Cdk activities responsible for initiating DNA replication (S-phase promoting factor or SPF) in Xenopus egg extracts.
  • To characterize the roles of different cyclin-Cdk complexes in supporting DNA replication.

Main Methods:

  • Affinity-depletion of Cdks from Xenopus egg extracts.
  • Assaying for S-phase promoting factor (SPF) activity in depleted extracts using recombinant cyclins.
  • Analyzing cyclin-Cdk complex composition in early Xenopus embryos.

Main Results:

  • Depletion of Cdks blocked DNA replication initiation; restored activity defined SPF.
  • Recombinant cyclins A and E, but not B, exhibited SPF activity.
  • Cyclin E1-Cdk2 complexes were sufficient for S-phase entry, while cyclin A-Cdc2 complexes provided additional SPF during S-phase.

Conclusions:

  • Cyclin E1-Cdk2 is sufficient for initiating DNA replication in early Xenopus embryos.
  • Cyclin A-Cdc2 contributes significant SPF activity as S-phase progresses.
  • Specific cyclin-Cdk complexes play distinct roles in regulating DNA replication during early development.

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