High mobility group proteins 1 and 2 can function as DNA-binding regulatory components for DNA-dependent protein kinase in vitro.
The DNA-dependent protein kinase (DNA-PK) holoenzyme consists of a 470-kDa catalytic subunit (DNA-PKcs), a DNA-binding regulatory component known as Ku protein, and double-stranded DNA (dsDNA) with ends. We previously reported that the activity of DNA-PK in vitro is stimulated by non-histone chromosomal high mobility group proteins (HMG) 1 and 2 comprising two similar repeats, termed domains A and B, and an acidic C-terminal. Here we demonstrate that in vitro HMG1 and 2 can completely replace Ku protein as the DNA-binding regulatory component of DNA-PK. DNA-PKcs and Ku protein were separately purified from Raji nuclear extracts, and reconstituted into the DNA-PK holoenzyme in the presence of dsDNA. DNA-PKcs alone catalyzed DNA-dependent phosphorylation at a very low but significant level, and HMG1 and 2 markedly stimulated the phosphorylation of alpha-casein and a specific peptide substrate in a DNA-dependent manner. The HMG2-domains (A+B) polypeptide devoid of the C-terminal acidic region was more effective for DNA-PKcs stimulation than the full-length HMG2, and HMG2-domain A and -domain B polypeptides. Anti(Ku protein) antibodies inhibited the DNA-dependent phosphorylation activity of the DNA-PKcs:Ku protein complex, but not that of DNA-PKcs alone or when it was complexed with HMG1 or 2. These results demonstrate that HMG1 and 2 can function as the DNA-binding regulatory component for DNA-PKcs in vitro, and imply that a conformational change of dsDNA, which is elicited by regulatory components, is important for the stimulation of DNA-PK activity of DNA-PKcs.
Yumoto
Y
Y
Department of Pathological Biochemistry, Medical Research Institute, Tokyo Medical and Dental University, Chiyoda-ku, Tokyo 101-0062, Japan.
Shirakawa
H
H
Yoshida
M
M
Suwa
A
A
Watanabe
F
F
Teraoka
H
H
D000595:Amino Acid Sequence; D000818:Animals; D034961:Antigens, Nuclear; D002417:Cattle; D004247:DNA / Q000378:metabolism*; D004265:DNA Helicases; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins / Q000378:metabolism; D004789:Enzyme Activation; D006609:High Mobility Group Proteins / Q000378:metabolism*; D000072200:Ku Autoantigen; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*
D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D006609:High Mobility Group Proteins; D009687:Nuclear Proteins; D004247:DNA; D051747:DNA-Activated Protein Kinase; D017346:Protein Serine-Threonine Kinases; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen