The zab domain of the human RNA editing enzyme ADAR1 recognizes Z-DNA when surrounded by B-DNA.
The Zab domain of the editing enzyme ADAR1 binds tightly and specifically to Z-DNA stabilized by bromination or supercoiling. A stoichiometric amount of protein has been shown to convert a substrate of suitable sequence to the Z form, as demonstrated by a characteristic change in the CD spectrum of the DNA. Now we show that Zab can bind not only to isolated Z-forming d(CG)(n) sequences but also to d(CG)(n) embedded in B-DNA. The binding of Zab to such sequences results in a complex including Z-DNA, B-DNA, and two B-Z junctions. In this complex, the d(CG)(n) sequence, but not the flanking region, is in the Z conformation. The presence of Z-DNA was detected by cleavage with a Z-DNA specific nuclease, by undermethylation using Z-DNA sensitive SssI methylase, and by circular dichroism. It is possible that Zab binds to B-DNA with low affinity and flips any favorable sequence into Z-DNA, resulting in a high affinity complex. Alternatively, Zab may capture Z-DNA that exists transiently in solution. The binding of Zab to potential as well as established Z-DNA segments suggests that the range of biological substrates might be wider than previously thought.
Kim
Y G
YG
Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Lowenhaupt
K
K
Maas
S
S
Herbert
A
A
Schwartz
T
T
Rich
A
A
D000243:Adenosine Deaminase / Q000737:chemistry / Q000378:metabolism*; D001483:Base Sequence; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007536:Isomerism; D010957:Plasmids; D017393:RNA Editing; D016601:RNA-Binding Proteins
D004268:DNA-Binding Proteins; D016601:RNA-Binding Proteins; D004247:DNA; C567955:ADARB1 protein, human; D000243:Adenosine Deaminase