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1: Nature. 2003 Jul 3;424(6944):103-7. Epub 2003 Jun 18.
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Processive AID-catalysed cytosine deamination on single-stranded DNA simulates somatic hypermutation.

Pham P, Bransteitter R, Petruska J, Goodman MF.

Department of Biological Sciences, Hedco Molecular Biology Laboratories, University of Southern California, University Park, Los Angeles, California 90089-1340, USA.

Activation-induced cytidine deaminase (AID) is a protein required for B cells to undergo class switch recombination and somatic hypermutation (SHM)--two processes essential for producing high-affinity antibodies. Purified AID catalyses the deamination of C to U on single-stranded (ss)DNA. Here, we show in vitro that AID-catalysed C deaminations occur preferentially on 5' WRC sequences in accord with SHM spectra observed in vivo. Although about 98% of DNA clones suffer no mutations, most of the remaining mutated clones have 10-70 C to T transitions per clone. Therefore, AID carries out multiple C deaminations on individual DNA strands, rather than jumping from one strand to another. The avid binding of AID to ssDNA could result from its large net positive charge (+11) at pH 7.0, owing to a basic amino-terminal domain enriched in arginine and lysine. Furthermore, AID exhibits a 15-fold preference for C deamination on the non-transcribed DNA strand exposed by RNA polymerase than the transcribed strand protected as a RNA-DNA hybrid. These deamination results on ssDNA bear relevance to three characteristic features of SHM: preferential mutation at C sites within WRC hotspot sequences, the broad clonal mutagenic heterogeneity of antibody variable regions targeted for mutation, and the requirement for active transcription to obtain mutagenesis.

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PMID: 12819663 [PubMed - indexed for MEDLINE]