Activation-induced cytidine deaminase (AID) is essential for class-switch recombination (CSR) and somatic hypermutation (SHM). Mutants with changes in the C-terminal region of AID retain SHM but lose CSR activity. Here we describe five mutants with alterations in the N-terminal region of AID that caused selective deficiency in SHM but retained CSR, suggesting that the CSR and SHM activities of AID may dissociate via interaction of CSR- or SHM-specific cofactors with different domains of AID. Unlike cells expressing C-terminal AID mutants, B cells expressing N-terminal AID mutants had mutations in the switch micro region, indicating that such mutations are generated by reactions involved in CSR but not SHM. Thus, we propose that separate domains of AID interact with specific cofactors to regulate these two distinct genetic events in a target-specific way.

In the presence of Pd(II) salts, substitution reaction of aryl halides with potassium cyanide occurs readily which affords a simple and beneficial method for aryl cyanide synthesis.

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Cell extracts were prepared from Escherichia coli carrying colicin El plasmid. The DNA in extracts was almost exclusively closed-circular DNA of the plasmid. Labeled deoxyribonucleotides were incorporated into DNA