Gallo Angela, Keegan Liam P, Ring Gillian M, O'Connell Mary A
MRC Human Genetics Unit, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK.
EMBO J. 2003 Jul 1;22(13):3421-30. doi: 10.1093/emboj/cdg327.
In this report, we establish that Drosophila ADAR (adenosine deaminase acting on RNA) forms a dimer on double-stranded (ds) RNA, a process essential for editing activity. The minimum region required for dimerization is the N-terminus and dsRNA-binding domain 1 (dsRBD1). Single point mutations within dsRBD1 abolish RNA-binding activity and dimer formation. These mutations and glycerol gradient analysis indicate that binding to dsRNA is important for dimerization. However, dimerization can be uncoupled from dsRNA-binding activity, as a deletion of the N-terminus (amino acids 1-46) yields a monomeric ADAR that retains the ability to bind dsRNA but is inactive in an editing assay, demonstrating that ADAR is only active as a dimer. Different isoforms of ADAR with different editing activities can form heterodimers and this can have a significant effect on editing in vitro as well as in vivo. We propose a model for ADAR dimerization whereby ADAR monomers first contact dsRNA; however, it is only when the second monomer binds and a dimer is formed that deamination occurs.
在本报告中，我们证实果蝇中的ADAR（作用于RNA的腺苷脱氨酶）在双链（ds）RNA上形成二聚体，这是编辑活性所必需的过程。二聚化所需的最小区域是N端和双链RNA结合结构域1（dsRBD1）。dsRBD1内的单点突变会消除RNA结合活性和二聚体形成。这些突变和甘油梯度分析表明，与dsRNA的结合对二聚化很重要。然而，二聚化可以与dsRNA结合活性解偶联，因为N端（氨基酸1 - 46）的缺失产生了一种单体ADAR，它保留了结合dsRNA的能力，但在编辑试验中无活性，这表明ADAR仅作为二聚体具有活性。具有不同编辑活性的ADAR不同同工型可以形成异二聚体，这对体外和体内的编辑都有显著影响。我们提出了一个ADAR二聚化模型，即ADAR单体首先与dsRNA接触；然而，只有当第二个单体结合并形成二聚体时才会发生脱氨作用。
