A novel four zinc-finger protein targeted against p190(BcrAbl) fusion oncogene cDNA: utilisation of zinc-finger recognition codes

A three zinc-finger protein that binds specifically to the cDNA representing the unique fusion gene BcrAbl, associated with acute lymphoblastic leukaemia, has previously been characterised. At this breakpoint, a sequence homology of 8/9 bp exists between the BcrAbl (fusion) and c-Abl (parental) target sequences. We show that the three zinc-finger protein discriminates poorly between the fusion (BcrAbl) and parental (Abl) sequence (K(d)s of 42.8 and 65.1 nM, respectively). In order to improve the discriminatory properties of this protein, and to demonstrate the utility of current zinc-finger databases, we have added a fourth zinc-finger to the original three zinc-finger protein. This fourth finger recognises a 3 bp subsite derived from the Bcr portion of the breakpoint and is not present in c-Abl. This novel four finger protein, which now recognises a 12 bp sequence, demonstrates improved specific binding to BcrAbl (K(d) = 17 nM). More significantly we have shown that there is now enhanced discrimination between BcrAbl and Abl sequences by the four finger protein than the original three finger protein.