title: Identification of a stimulus-dependent DNase I hypersensitive site between the Ialpha and Calpha exons during immunoglobulin heavy chain class switch recombination.
abstract: The complete humoral response to foreign antigen depends upon two distinct recombination events within the heavy chain locus of immunoglobulin. The first recombination event takes place in what will become the antigen combining site of the antibody molecule, encoded by V, D and J segments. The second recombination event involves the looping-out of large spans of DNA which separate the various clusters of heavy chain exons which define the different immunoglobulin isotypes, or classes. While a great deal has been learned about the nature of the VDJ recombinase, very little is known about the nature of the class-switch recombinase. Using a cell system where class-switch recombination occurs primarily to the IgA locus, we have looked for stimulus-dependent changes in the chromatin structure of the IgA locus which might result from interactions between components of the recombinase and cis-elements within the region. We present evidence that strongly suggests that the class-switch recombinase interacts between the Ialpha and Calpha exons of IgA, just upstream of the highly reiterated DR1 and DR2 elements. However, although multiple potential SMAD-4 sites are located precisely within the DNase I hypersensitive site and 160 bp upstream of that site, we failed to detect any evidence of DNA/protein interactions near the hypersensitive site. Moreover, recombinant SMAD-3/4 proteins fail to interact with these sites with appreciable affinity in vitro. These data suggest that some other structural alteration at this site (e.g. RNA/DNA hybrid) may mediate the nuclease sensitivity.
authors.affiliation: Laboratory of Molecular Immunology, The Schepens Eye Research Institute and Committee on Immunology, Harvard University, 20 Staniford St., Boston, MA, USA. sjono@vision.eri.harvard.edu
authors.forename: S J
authors.initials: SJ
authors.lastname: Ono
authors.forename: G
authors.initials: G
authors.lastname: Zhou
authors.forename: A K
authors.initials: AK
authors.lastname: Tai
authors.forename: M
authors.initials: M
authors.lastname: Inaba
authors.forename: K
authors.initials: K
authors.lastname: Kinoshita
authors.forename: T
authors.initials: T
authors.lastname: Honjo
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D015139:Blotting, Southern; D023201:CD40 Ligand; D002460:Cell Line; D004254:DNA Nucleotidyltransferases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D003850:Deoxyribonuclease I / Q000378:metabolism*; D005091:Exons; D005434:Flow Cytometry; D007070:Immunoglobulin A / Q000235:genetics*; D017578:Immunoglobulin Class Switching; D007143:Immunoglobulin Heavy Chains / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D007134:Immunoglobulin Switch Region; D015847:Interleukin-4 / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000494:pharmacology; D008969:Molecular Sequence Data; D015534:Trans-Activators / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D045567:VDJ Recombinases
chemical_list: D004268:DNA-Binding Proteins; D007070:Immunoglobulin A; D007143:Immunoglobulin Heavy Chains; D008562:Membrane Glycoproteins; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D023201:CD40 Ligand; D015847:Interleukin-4; D004254:DNA Nucleotidyltransferases; D045567:VDJ Recombinases; C069600:cisA recombinase; D003850:Deoxyribonuclease I