Caught in the act: binding of Ku and PARP to MARs reveals novel aspects of their functional interaction.
Specific regions of eukaryotic genomic DNA that exhibit high-affinity binding to the nuclear matrix in vitro are called matrix attachment regions (MARs) and are implicated in the loop domain organization of chromatin. Small regions possessing high base unpairing potential within these MARs are referred to as base unpairing regions (BURs). BUR-affinity chromatographic separations of proteins from breast cancer cells yielded, almost exclusively, a mixture of poly (ADP-ribose) polymerase (PARP) and DNA-dependent protein kinase (DNA-PK), two nuclear enzymes that are implicated in the cellular response to DNA damage. Contrary to the long-held notion that PARP and Ku autoantigen, the DNA-binding heterodimeric subunit of DNA-PK, bind only to DNA ends, recently we have shown that both proteins individually bind BURs with high affinity and specificity in an end-independent manner. Furthermore, Ku autoantigen forms a molecular complex with PARP in the absence of DNA, and the physical association of these proteins synergistically enhanced their BUR-binding activity. Autoribosylation of PARP abolished its association with Ku autoantigen and BUR-binding activity. These findings have, for the first time, provided a molecular link toward elucidating the functional interaction between PARP and DNA-PK. The identification of MARs as their common binding target suggests a novel role for these enzymes in the modulation of chromatin structure and function.
Galande
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S
Life Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley 94706, USA.
Kohwi-Shigematsu
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T
D034961:Antigens, Nuclear; D001324:Autoantigens / Q000378:metabolism* / Q000502:physiology; D001943:Breast Neoplasms / Q000378:metabolism; D004265:DNA Helicases; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D005260:Female; D006801:Humans; D000072200:Ku Autoantigen; D036961:Matrix Attachment Region Binding Proteins; D009363:Neoplasm Proteins / Q000378:metabolism; D015530:Nuclear Matrix / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism* / Q000502:physiology; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism* / Q000502:physiology; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism
C097879:114 kDa MAR-binding protein, human; D034961:Antigens, Nuclear; D001324:Autoantigens; D004268:DNA-Binding Proteins; D036961:Matrix Attachment Region Binding Proteins; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011065:Poly(ADP-ribose) Polymerases; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen