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Mol Cell. 2004 Oct 22;16(2):163-71.

Mismatch recognition and uracil excision provide complementary paths to both Ig switching and the A/T-focused phase of somatic mutation.

Author information

1
Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom. car@mrc-lmb.cam.ac.uk

Abstract

AID-mediated deamination of dC residues within the immunoglobulin locus generates dU:dG lesions whose resolution leads to class-switch recombination and somatic hypermutation. The dU:dG pair is a mismatch and comprises a base foreign to DNA and is, thus, recognized by proteins from both base excision (uracil-DNA glycosylase, UNG) and mismatch recognition (MSH2/MSH6) pathways. Strikingly, while antibody diversification is perturbed by single deficiency in either UNG or MSH2, combined UNG/MSH2 deficiency leads to a total ablation both of switch recombination and of IgV hypermutation at dA:dT pairs. The initiating dU:dG lesions appear not to be recognized and are simply replicated over. The results indicate that the major pathway for switch recombination occurs through uracil excision with mismatch recognition of dU:dG providing a backup; the second phase of hypermutation (essentially introducing mutations solely at dA:dT pairs) is triggered by mismatch recognition of the dU:dG lesion with uracil excision providing a backup.

PMID:
15494304
DOI:
10.1016/j.molcel.2004.10.011
[Indexed for MEDLINE]
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