Figure 17-30. Mechanisms controlling S-phase initiation in animal cells.

Figure 17-30Mechanisms controlling S-phase initiation in animal cells

G1-Cdk activity (cyclin D-Cdk4) initiates Rb phosphorylation. This inactivates Rb, freeing E2F to activate the transcription of S-phase genes, including the genes for a G1/S-cyclin (cyclin E) and S-cyclin (cyclin A). The resulting appearance of G1/S-Cdk and S-Cdk activities further enhances Rb phosphorylation, forming a positive feedback loop. E2F acts back to stimulate the transcription of its own gene, forming another positive feedback loop.

From: Intracellular Control of Cell-Cycle Events

Cover of Molecular Biology of the Cell
Molecular Biology of the Cell. 4th edition.
Alberts B, Johnson A, Lewis J, et al.
New York: Garland Science; 2002.
Copyright © 2002, Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter; Copyright © 1983, 1989, 1994, Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff, Keith Roberts, and James D. Watson .

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