FIGURE 4.

DNA-PK phosphorylates linker histones in vitro and in a nucleosome setting. Lanes 1 and 2 show an autoradiograph of an SDS-PAGE of HeLa mononucleosomes lacking (lane 1) or containing histone H1 (lane 2) upon phosphorylation by DNA-PK using [γ-³²P]ATP. Lanes 3–5 show an autoradiograph of an SDS-PAGE of purified HeLa histone H2A.X, histone H1, and H3-H4 tetramers phosphorylated by DNA-PK using [γ-³²P]ATP. Artemis (Ar) was used as a substrate to serve as a positive control for these reactions. The high molecular weight bands correspond to autophosphorylated DNA-PK subunits, the DNA-PK catalytic subunit, and Ku 70/80.