Sohail Anjum, Klapacz Joanna, Samaranayake Mala, Ullah Asad, Bhagwat Ashok S
Department of Chemistry, Wayne State University, Detroit, MI 48202, USA.
Nucleic Acids Res. 2003 Jun 15;31(12):2990-4. doi: 10.1093/nar/gkg464.
Activation-induced cytidine deaminase (AID) is required for the maturation of antibodies in higher vertebrates, where it promotes somatic hypermutation (SHM), class switch recombination and gene conversion. While it is known that SHM requires high levels of transcription of the target genes, it is unclear whether this is because AID targets transcribed genes. We show here that the human AID promotes C to T mutations in Escherichia coli which are stimulated by transcription. The mutations are strand-biased and occur preferentially in the non-transcribed strand of the target gene. Human AID purified from E.coli is active without prior treatment with a ribonuclease and deaminates cytosines in plasmid DNA in vitro. Further, the action of this enzyme is greatly stimulated by the transcription of the target gene in a strand-dependent fashion. These results confirm the prediction that AID may act directly on DNA and show that it can act on transcribing DNA in the absence of specialized DNA structures such as R-loops. It suggests that AID may be recruited to variable genes through transcription without the assistance of other proteins and that the strand bias in SHM may be caused by the preference of AID for the non-transcribed strand.
激活诱导的胞苷脱氨酶（AID）是高等脊椎动物抗体成熟所必需的，它在其中促进体细胞高频突变（SHM）、类别转换重组和基因转换。虽然已知SHM需要靶基因的高水平转录，但尚不清楚这是否是因为AID靶向转录基因。我们在此表明，人AID在大肠杆菌中促进C到T的突变，这种突变受转录刺激。这些突变具有链偏向性，并且优先发生在靶基因的非转录链上。从大肠杆菌中纯化的人AID无需事先用核糖核酸酶处理就具有活性，并且在体外使质粒DNA中的胞嘧啶脱氨。此外，该酶的作用以链依赖的方式受到靶基因转录的极大刺激。这些结果证实了AID可能直接作用于DNA的预测，并表明它可以在不存在诸如R环等特殊DNA结构的情况下作用于转录中的DNA。这表明AID可能在没有其他蛋白质协助的情况下通过转录被募集到可变基因，并且SHM中的链偏向可能是由AID对非转录链的偏好引起的。
