title: Altered spectra of hypermutation in DNA repair-deficient mice.
abstract: Affinity maturation of the humoral immune response is based on the ability of immunoglobulin variable genes to undergo a process of rapid and extensive somatic mutation followed by antigenic selection for antibodies with higher affinity. While the behaviour of this somatic hypermutation phenomenon has been well characterized over the last 20 years, the molecular mechanism responsible for inserting mutations has remained shrouded. To better understand this mechanism, we studied the interplay between hypermutation and other DNA associated activities such as DNA repair. There was no effect on the frequency and pattern of hypermutation in mice deficient for nucleotide excision repair, base excision repair and ataxia-telangiectasia mutated gene repair of double strand breaks. However, variable genes from mice lacking some components of mismatch repair had an increased frequency of tandem mutations and had more mutations of G and C nucleotides. These results suggest that the DNA polymerase(s) involved in the hypermutation pathway produces a unique spectra of mutations, which is then altered by mismatch repair and antigenic selection. We, also describe the differential pattern of expression of some nuclear DNA polymerases in hypermutating versus non-hypermutating B lymphocytes. The rapidly dividing germinal centre B cells expressed DNA polymerases alpha, beta, delta, epsilon and zeta, whereas the resting non-germinal centre cells did not express polymerases alpha or epsilon at detectable levels, although they did express polymerases beta, delta and zeta. The lack of expression of polymerase epsilon in the non-germinal centre cells suggests that this enzyme has a critical role in chromosomal replication but does not participate in DNA repair in these cells.
authors.affiliation: Laboratory of Molecular Genetics, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224-6825, USA.
authors.forename: D B
authors.initials: DB
authors.lastname: Winter
authors.forename: P J
authors.initials: PJ
authors.lastname: Gearhart
mesh_terms: D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D020137:Base Pair Mismatch; D018797:Cell Cycle Proteins; D004260:DNA Repair / Q000235:genetics*; D004268:DNA-Binding Proteins; D004259:DNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D025521:Tumor Suppressor Proteins
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D025521:Tumor Suppressor Proteins; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; D017346:Protein Serine-Threonine Kinases; D004259:DNA-Directed DNA Polymerase