HIGHER-ORDER CHROMATIN STRUCTURE-DEPENDENT REPAIR OF DNA DOUBLE-STRAND BREAKS - INVOLVEMENT OF THE V(D)J RECOMBINATION DOUBLE-STRAND BREAK REPAIR PATHWAY

Repair of DNA double-strand breaks (DSBs) is linked to the V(D)J recom bination pathway through investigations of radiation-sensitive mutants . Here we report a possible association between the distribution of DS Bs within higher-order chromatin structures and this pathway. Both mur ine severe combined immunodeficient (SCID) and Chinese hamster XR-1 ce lls exhibit defective DNA DSB repair and defective V(D)J recombination . The DSB repair defect is not complete, with only a subset of slowly repairing lesions affected by the mutations in these cell lines. We us ed a modified neutral filter elution procedure which retained elements of higher-order chromatin structures, namely nuclear matrix-DNA inter actions. X-ray-induced DSBs that occurred as multiples within looped D NA structures were nonrepairable in SCID and XR-1 cells. In contrast, these lesions were repaired in radioresistant wild-type cells. Cell li nes complemented with human DNA containing the respective complementin g genes (XRCC7 and XRCC4) showed an increased rate of DSB repair. Thes e results agree with previous findings with xrs5 cells (a member of th e XRCC5 group). Xrs5 cells are defective for the Ku p80 subunit of the V(D)J recombination complex and show repair and V(D)J recombination d efects similar to those of SCID and XR-1 cells. (C) 1998 by Radiation Research Society.