Study of the higher eukaryotic gene function CDK2 using fission yeast

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• In fission yeast (Schizosaccharomyces pombe), cdc2 is essential for both G1 entry and G2/M transition.
• Higher eukaryotes utilize cdc2-like genes, including CDK2, for these cell cycle functions.
• Previous studies showed that CDK2 cannot complement temperature-sensitive cdc2 mutations in S. pombe.

Purpose of the Study:

• To investigate the specific functions of CDK2 in the S. pombe cell cycle.
• To determine if CDK2 can substitute for cdc2 functions, particularly in G1 and G2/M phases.
• To identify novel genes or cdc2 interactions involving CDK2.

Main Methods:

• Overexpression of human (HsCDK2) and Xenopus (XlCDK2) CDK2 homologs in S. pombe.
• Complementation analysis of cdc2 temperature-sensitive mutants using XlCDK2.
• Screening for XlCDK2-dependent mutants.

Main Results:

• HsCDK2 overexpression caused G2/M cell cycle arrest, indicating interference with mitotic events.
• XlCDK2 could rescue the G1 block but not the G2 block of a cdc2-M26 ts strain.
• An inactive XlCDK2 mutant (XlCDK2-R33) failed to rescue the G1 block, highlighting the necessity of kinase activity for G1 progression.
• Selected XlCDK2-dependent mutants were identified as cdc2 mutants specifically altered in G2/M function.

Conclusions:

• Xenopus CDK2 (XlCDK2) can influence both G1/S and G2/M transitions mediated by cdc2 in S. pombe.
• The protein kinase activity of CDK2 is required for entry into the cell cycle (G1 phase).
• CDK2 homologs can functionally interact with or partially substitute for cdc2, particularly in G1 progression.