G2 phase is second gap phase dedicated to growth, quality surveillance, and accumulation of components required for mitosis. After S phase completes DNA synthesis, cells continue protein synthesis, particularly tubulin alpha/beta heterodimers and gamma-tubulin ring complex proteins for spindle assembly, histone variants H2AZ for chromatin stability, and membrane lipid synthesis for organelle expansion. Centrosomes duplicated during S phase mature in G2 by recruitment of pericentriolar material including pericentrin, Cep192, and Cdk5Rap2, acquiring ability to nucleate large astral microtubule arrays. Mitochondria undergo fusion driven by mitofusins to enhance ATP production for mitosis. Simultaneously DNA damage checkpoint kinase ATR monitors incomplete replication intermediates and stalled forks, maintaining cyclin B-CDK1 inactive via Wee1 mediated Tyr15 phosphorylation until genome fully duplicated. Transcription of mitotic cyclin B and Polo-like kinase rises, preparing wave of mitotic entry. G2 thus bridges synthesis and segregation, ensuring daughters inherit intact genome and sufficient cytoplasm. This circuitry is highly conserved across eukaryotes, integrating growth factor signals, DNA damage surveillance, and developmental cues, and its disruption frequently underlies oncogenesis, providing targets for checkpoint inhibitors and cancer therapeutics.
Ref:
Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 17, G2 as Preparation for M Phase.
