BRCA1 (red) is found with replicating heterochromatic DNA (green) in mouse cells. Three views of a single cluster of centromeres are shown on the right.
Repair is the function usually ascribed to BRCA1, which accumulates at damaged DNA in irradiated cells. But undamaged cells also have nuclear BRCA1 foci. They appear mostly during S phase, but because the foci do not have a clear-cut overlap with the majority of replicating DNA, their function has been difficult to explain.
The new results reveal an association of nuclear BRCA1 foci specifically with subsets of replicating heterochromatin. In mouse cells, highly heterochromatic centromeres gather in easily stained clusters known as chromocenters. In cells that are replicating these bright blocks, the...
