Absence of DNA Polymerase η Reveals Targeting of C Mutations on the Nontranscribed Strand in Immunoglobulin Switch Regions

Xianmin Zeng, George A. Negrete, Cynthia Kasmer, William W. Yang, Patricia J. Gearhart

Research output: Contribution to journalArticlepeer-review

68 Scopus citations


Activation-induced cytosine deaminase preferentially deaminates C in DNA on the nontranscribed strand in vitro, which theoretically should produce a large increase in mutations of C during hypermutation of immunoglobulin genes. However, a bias for C mutations has not been observed among the mutations in variable genes. Therefore, we examined mutations in the μ and γ switch regions, which can form stable secondary structures, to look for C mutations. To further simplify the pattern, mutations were studied in the absence of DNA polymerase (pol) η, which may produce substitutions of nucleotides downstream of C. DNA from lymphocytes of patients with xeroderma pigmentosum variant (XP-V) disease, whose polymerase η is defective, had the same frequency of switching to all four γ isotypes and hypermutation in μ-γ switch sites (0.5% mutations per basepair) as control subjects. There were fewer mutations of A and T bases in the XP-V clones, similar to variable gene mutations from these patients, which confirms that polymerase η produces substitutions opposite A and T. Most importantly, the absence of polymerase η revealed an increase in C mutations on the nontranscribed strand. This data shows for the first time that C is preferentially mutated in vivo and pol η generates hypermutation in the μ and γ switch regions.

Original languageEnglish (US)
Pages (from-to)917-924
Number of pages8
JournalJournal of Experimental Medicine
Issue number7
StatePublished - Apr 5 2004
Externally publishedYes


  • Activation-induced cytosine deaminase
  • Gap-filling repair
  • Somatic hypermutation
  • Translesion replication
  • Xeroderma pigmentosum variant

ASJC Scopus subject areas

  • Immunology and Allergy
  • Immunology


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