Figure 17-21. Evidence from cell-fusion experiments for a rereplication block.

Figure 17-21Evidence from cell-fusion experiments for a rereplication block

These experiments were carried out in 1970 in cultured mammalian cells. (A) The results show that S-phase cytoplasm contains factors that drive a G1 nucleus directly into DNA synthesis. (B) A G2 nucleus, having already replicated its DNA, is refractory to these factors. (C) Fusion of a G2 cell with a G1 cell does not drive the G1 nucleus into DNA synthesis, indicating that the cytoplasmic factors for DNA replication that were present in the S-phase cell disappear when the cell moves from S phase into G2. (Adapted from R.T. Johnson and P.N. Rao, Nature 226:717–722, 1970.)

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 .

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.