A 6 bp Z-DNA hairpin binds two Z alpha domains from the human RNA editing enzyme ADAR1

The Z alpha domain of the human RNA editing enzyme double-stranded RNA deam inase I (ADAR1) binds to left-handed Z-DNA with high affinity. We found by analytical ultracentrifugation and CD spectroscopy that two Z alpha domains bind to one d(CG)(3)T-4(CG)(3) hairpin which contains a stem of six base p airs in the Z-DNA conformation, Both wild-type Z alpha and a C125S mutant s how a mean dissociation constant of 30 nM as measured by surface plasmon re sonance and analytical ultracentrifugation. Our data suggest that short (gr eater than or equal to 6 bp) segments of Z-DNA within a gene are able to re cruit two ADAR1 enzymes to that particular site, (C) 1999 Federation of Eur opean Biochemical Societies.