THE DNA-BINDING DOMAIN OF THE HUMAN C-ABL TYROSINE KINASE PREFERENTIALLY BINDS TO DNA-SEQUENCES CONTAINING AN AAC MOTIF AND TO DISTORTED DNA STRUCTURES

The c-Abl tyrosine kinase protein is implicated in the signaling pathw ay as well as in transcription, DNA repair, apoptosis, and several oth er vital biological processes essential for cell proliferation or diff erentiation. The interaction of c-Abl with DNA is important for some o f these functions, but the exact nature of this interaction is still a matter of controversy. The present study addresses the DNA-binding pr operties of the human c-Abl protein. Using CASTing experiments, the co nsensus binding site 5'-A(A/C)AACAA(A/C) was determined. The central h ighly conserved AAC triplet appears to constitute the crucial core ele ment in the binding sequences of the c-Abl protein. The c-Abl DNA-bind ing domain recognizes specific sequences and interacts with deformed D NA structures such as four-way junctions and bubble DNA containing a l arge single-stranded loop, as determined by electromobility shift assa y, melting temperature studies, and binding to specific oligonucleotid es covalently Linked to beads. Additional competition experiments sugg est that the interaction mainly involves contacts within the minor gro ove of the double helix. The DNA-binding properties of c-Abl are remin iscent of those of high-mobility group (HMG)-like proteins such as LEF -1 and SRY. However, the circular permutation and ring closure assays and DNA unwinding experiments reveal that, unlike HMGs, c-Abl does not bend its target sequence. In addition, it is shown that the protein p otentiates the DNA relaxation activity of topoisomerase I. These findi ngs indicate that the interaction of c-Abl with DNA is both sequence-s elective and structure-dependent.