FIG. 5.

Proposed model of reciprocal regulation of end access by DNA-PK's autophosphorylation status. Panels 1 to 6 represent distinct conformations induced by autophosphorylation. Certainly, we have no information that these particular sites are physically associated with DNA ends; we are proposing that a conformational change induces the described structures that regulate end processing. Asterisks denote phosphorylated sites (either ABCDE or PQR). The hypothesized model of a continuous conformational change from nonphosphorylation to complete autophosphorylation is presented in panels 1 to 3. The bottom panels represent the proposed configuration of the three alanine mutants: panel 4, ABCDE>A; panel 5, PQR>A; and panel 6, ABCDE+PQR>A.