Figure 1

Timing of replication correlates with chromatin location. HeLa cells were briefly pulsed with Cy3-dUTP to mark actively replicating regions of chromatin, then fixed and imaged on a fluorescence microscope. The cell on the left is late in S-phase and preferentially replicating heterochromatic regions, with those in the nuclear periphery marked by arrowheads. The cell on the right is at an earlier stage of S phase, when predominantly internal chromatin is replicated. See [15] and references therein for further details. Scale bar= 5 μm.