Amino acid substitutions in the DNA-PKcs constructs.

1. Serine (S) and threonine (T) were replaced with alanine (A) at S2056 and T2609 cluster sites.2. V3-KC23 mutant carries a frame-shift at position of amino acid 3715 that results in truncation of the protein after 10 amino acids and loss of the entire PI3K kinase domain.3. In V3-KD51 mutant aspartic acid (D) at 3921 is replaced with asparagine (N).4. N: Normal; S: Slightly sensitive; SS, Sensitive; SSS: Very sensitive. Levels are from a previous report on survival responses from this laboratory; Sensitivities marked by the * were those confirmed independently in the present study.