DNA-dependent protein kinase (DNA-PK) plays an important role in DNA double-strand break (DSB) repair and V(D)J recombination. We have isolated a new X-ray-sensitive CHO cell line, XR-C1, which is impaired in DSB repair and which was assigned to complementation group 7, the group that is defective in the XRCC7/SCID(Prkdc) gene encoding the catalytic subunit of DNA-PK (DNA-PKcs). Consistent with this complementation analysis, XR-C1 cells lacked detectable DNA-PKcs protein, did not display DNA-PK catalytic activity and were complemented by the introduction of a single human chromosome 8 (providing the Prkdc gene). The impact of the XR-C1 mutation on V(D)J recombination was quite different from that found in most rodent cells defective in DNA-PKcs, which are preferentially blocked in coding joint formation, whereas XR-C1 cells were defective in forming both coding and signal joints. These results suggest that DMA-PKcs is required for both coding and signal joint formation during V(D)J recombination and that the XR-C1 mutant cell line may prove to be a useful tool in understanding this pathway.
Bibliographical noteFunding Information:
We would like to thank Laura Wetselaar and Marjolein Sonneveld for their skilful technical assistance, Drs Dik van Gent and Roland Kanaar for discussion, and we wish to acknowledge the help of Dr G.W.C.T.Verhaegh with pilot experiments on complementation analysis of XR-C1 cells. We also would like to thank Graeme C.M.Smith, Nicholas D.Lakin and David Gell for advice on performing DNA-PK assays. This work was supported by European Union Grants F14PCT90010, BMH1-CT93 1510, a grant from the Cancer Research Campaign and a grant AI35763 (E.A.H.) from the National Institutes of Health. E.A.H. is a Leukemia Scholar of America.