IDENTIFICATION OF A NONSENSE MUTATION IN THE CARBOXYL-TERMINAL REGIONOF DNA-DEPENDENT PROTEIN-KINASE CATALYTIC SUBUNIT IN THE SCID MOUSE

DNA-dependent protein kinase (DNA-PK) consists of a heterodimeric prot ein (Ku) and a large catalytic subunit (DNA-PKcs). The Ku protein has double-stranded DNA end-binding activity that serves to recruit the co mplex to DNA ends. Despite having serine/threonine protein kinase acti vity, DNA-PKcs falls into the phosphatidylinositol 3-kinase superfamil y. DNA-PK functions in DNA double-strand break repair and V(D)J recomb ination, and recent evidence has shown that mouse scid cells are defec tive in DNA-PKcs. In this study we have cloned the cDNA for the carbox yl-terminal region of DNA-PKcs in rodent cells and identifed the exist ence of two differently spliced products in human cells. We show that DNA-PKcs maps to the same chromosomal region as the mouse scid gene, s cid cells contain approximately wild-type levels of DNA-PKcs transcrip ts, whereas the V-3 cell line, which is also defective in DNA-PKcs, co ntains very reduced transcript levels. Sequence comparison of the carb oxyl-terminal region of scid and wild-type mouse cells enabled us to i dentify a nonsense mutation within a highly conserved region of the ge ne in mouse scid cells. This represents a strong candidate for the ina ctivating mutation in DNA-PKcs in the scid mouse.