title: Quantitative regulation of class switch recombination by switch region transcription.
abstract: The isotype specificity of immunoglobulin (Ig) class switching is regulated by a cytokine which induces transcription of a specific switch (S) region, giving rise to so-called germline transcripts. Although previous studies have demonstrated that germline transcription of an S region is required for class switch recombination (CSR) of that particular S region, it has not been shown whether the level of S region transcription affects the efficiency of CSR. We addressed this question by using an artificial DNA construct containing a constitutively transcribed mu switch (Smu) region and an alpha switch (Salpha) region driven by a tetracycline-responsive promoter. The construct was introduced into a switch-inducible B lymphoma line and the quantitative correlation between Salpha region transcription and class switching efficiency was evaluated. The level of Salpha transcription was linearly correlated with CSR efficiency, reaching a plateau at saturation. On the other hand, we failed to obtain the evidence to support involvement of either RNA-DNA heteroduplex or trans germline transcripts in CSR. Taken together, it is likely that S region transcription and/or transcript processing in situ may be required for CSR. We propose that because of the unusual properties of S region DNA, transcription induces the DNA to transiently be single stranded, permitting secondary structure(s) to form. Such structures may be recognition targets of a putative class switch recombinase.
authors.affiliation: Department of Medical Chemistry, Graduate School of Medicine, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: C G
authors.initials: CG
authors.lastname: Lee
authors.forename: K
authors.initials: K
authors.lastname: Kinoshita
authors.forename: A
authors.initials: A
authors.lastname: Arudchandran
authors.forename: S M
authors.initials: SM
authors.lastname: Cerritelli
authors.forename: R J
authors.initials: RJ
authors.lastname: Crouch
authors.forename: T
authors.initials: T
authors.lastname: Honjo
mesh_terms: D000107:Acetylation; D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000737:chemistry / Q000235:genetics; D004254:DNA Nucleotidyltransferases / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D029968:Escherichia coli Proteins; D006657:Histones / Q000378:metabolism; D007134:Immunoglobulin Switch Region / Q000235:genetics*; D019426:Integrases; D016393:Lymphoma, B-Cell / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D045522:Recombinases; D011995:Recombination, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D017931:DNA Primers; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D006657:Histones; D045522:Recombinases; D004247:DNA; D004254:DNA Nucleotidyltransferases; D019426:Integrases; C115006:integron integrase IntI1