Aggregative organization enhances the DNA end-joining process that is mediated by DNA-dependent protein kinase.

The occurrence of DNA double-strand breaks in the nucleus provokes in its structural organization a large-scale alteration whose molecular basis is still mostly unclear. Here, we show that double-strand breaks trigger preferential assembly of nucleoproteins in human cellular fractions and that they mediate the separation of large protein-DNA aggregates from aqueous solution. The interaction among the aggregative nucleoproteins presents a dynamic condition that allows the effective interaction of nucleoproteins with external molecules like free ATP and facilitates intrinsic DNA end-joining activity. This aggregative organization is functionally coacervate-like. The key component is DNA-dependent protein kinase (DNA-PK), which can be characterized as a DNA-specific aggregation factor as well as a nuclear scaffold/matrix-interactive factor. In the context of aggregation, the kinase activity of DNA-PK is essential for efficient DNA end-joining. The massive and functional concentration of nucleoproteins on DNA in vitro may represent a possible status of nuclear dynamics in vivo, which probably includes the DNA-PK-dependent response to multiple double-strand breaks.