Specific Expression of Activation-induced Cytidine Deaminase (AID), a Novel Member of the RNA-editing Deaminase Family in Germinal Center B Cells

We have identified a novel gene referred to asactivation-induced deaminase (AID) by subtraction of cDNAs derived from switch-induced and uninduced murine B lymphoma CH12F3-2 cells, more than 80% of which switch exclusively to IgA upon stimulation. The amino acid sequence encoded by AID cDNA is homologous to that of apolipoprotein B (apoB) mRNA-editing enzyme, catalytic polypeptide 1 (APOBEC-1), a type of cytidine deaminase that constitutes a catalytic subunit for the apoB mRNA-editing complex. In vitro experiments using a glutathione S-transferase AID fusion protein revealed significant cytidine deaminase activity that is blocked by tetrahydrouridine and by zinc chelation. However, AID alone did neither demonstrate activity in C to U editing of apoB mRNA nor bind to AU-rich RNA targets. AID mRNA expression is induced in splenic B cells that were activated in vitro or by immunizations with sheep red blood cells. In situ hybridization of immunized spleen sections revealed the restricted expression of AID mRNA in developing germinal centers in which modulation of immunoglobulin gene information through somatic hypermutation and class switch recombination takes place. Taken together, these findings suggest that AID is a new member of the RNA-editing deaminase family and may play a role in genetic events in the germinal center B cell. We have identified a novel gene referred to asactivation-induced deaminase (AID) by subtraction of cDNAs derived from switch-induced and uninduced murine B lymphoma CH12F3-2 cells, more than 80% of which switch exclusively to IgA upon stimulation. The amino acid sequence encoded by AID cDNA is homologous to that of apolipoprotein B (apoB) mRNA-editing enzyme, catalytic polypeptide 1 (APOBEC-1), a type of cytidine deaminase that constitutes a catalytic subunit for the apoB mRNA-editing complex. In vitro experiments using a glutathione S-transferase AID fusion protein revealed significant cytidine deaminase activity that is blocked by tetrahydrouridine and by zinc chelation. However, AID alone did neither demonstrate activity in C to U editing of apoB mRNA nor bind to AU-rich RNA targets. AID mRNA expression is induced in splenic B cells that were activated in vitro or by immunizations with sheep red blood cells. In situ hybridization of immunized spleen sections revealed the restricted expression of AID mRNA in developing germinal centers in which modulation of immunoglobulin gene information through somatic hypermutation and class switch recombination takes place. Taken together, these findings suggest that AID is a new member of the RNA-editing deaminase family and may play a role in genetic events in the germinal center B cell. The germinal center (GC) 1The abbreviations used are: GC, germinal center; CSR, class switch recombination; apoB, apolipoprotein B; APOBEC-1, apoB mRNAediting enzyme, catalytic polypeptide 1; CD40L, CD40 ligand; GST, glutathione S-transferase; THU, tetrahydrouridine; LPS, lipopolysaccharide; RBC, red blood cells; SRBC, sheep RBC; GAPDH, glyceraldehydehyde-3-phosphate dehydrogenase; CHX, cycloheximide; IL, interleukin; TGF, transforming growth factor; RT-PCR, reverse transcription-polymerase chain reaction; kb, kilobase(s).1The abbreviations used are: GC, germinal center; CSR, class switch recombination; apoB, apolipoprotein B; APOBEC-1, apoB mRNAediting enzyme, catalytic polypeptide 1; CD40L, CD40 ligand; GST, glutathione S-transferase; THU, tetrahydrouridine; LPS, lipopolysaccharide; RBC, red blood cells; SRBC, sheep RBC; GAPDH, glyceraldehydehyde-3-phosphate dehydrogenase; CHX, cycloheximide; IL, interleukin; TGF, transforming growth factor; RT-PCR, reverse transcription-polymerase chain reaction; kb, kilobase(s). constitutes a highly specialized microenvironment required for the final maturation step of naive B cells toward antigen-specific memory cells or long-lived plasma cells (1Smith K.G. Light A. Nossal G.J. Tarlinton D.M. EMBO. J. 1997; 16: 2996-3006Crossref PubMed Scopus (333) Google Scholar, 2George J. Claflin L. Semin. Immunol. 1992; 4: 11-17PubMed Google Scholar). Two prominent alterations of immunoglobulin gene information are known to occur in this microenvironment (3Jacob J. Kassir R. Kelsoe G. J. Exp. Med. 1991; 173: 1165-1175Crossref PubMed Scopus (591) Google Scholar, 4Kraal G. Weissman I.L. Butcher E.C. Adv. Exp. Med. Biol. 1985; 186: 145-151PubMed Google Scholar, 5Berek C. Berger A. Apel M. Cell. 1991; 67: 1121-1129Abstract Full Text PDF PubMed Scopus (748) Google Scholar). First, accumulation of massive point mutations in the variable region exon, a process refer to as somatic hypermutation (6Neuberger M.S. Milstein C. Curr. Opin. Immunol. 1995; 7: 248-254Crossref PubMed Scopus (249) Google Scholar), gives rise to affinity maturation of antibody in association with selection of B cells expressing high affinity immunoglobulins on their surface (7Sablitzky F. Wildner G. Rajewsky K. EMBO J. 1985; 4: 345-350Crossref PubMed Scopus (108) Google Scholar, 8Kocks C. Rajewsky K. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 8206-8210Crossref PubMed Scopus (147) Google Scholar). Second, class switch recombination (CSR) replaces the exons encoding the heavy chain constant region (9Lorenz M. Radbruch A. Curr. Top. Microbiol. Immunol. 1996; 217: 151-169PubMed Google Scholar), which determines effector functions of the antibody including complement fixation. These two alterations of immunoglobulin gene information are critical for accounting for an effective humoral response to harmful microbes. The molecular mechanisms for these genetic events remain to be elucidated despite intensive study.To dissect the molecular mechanism of class switching, we have isolated a murine B lymphoma clone CH12F3-2 in which CSR from IgM to IgA begins to occur within a few hours after stimulation with IL-4, TGF-β, and CD40L, giving rise to more than 80% IgA+ cells (10Kinoshita K. Tashiro J. Tomita S. Lee Chung-Gi Honjo T. Immunity. 1998; 9: 349-358Abstract Full Text Full Text PDF Scopus (67) Google Scholar, 11Lee C.G. Kondo S. Honjo T. Curr. Biol. 1998; 8: 227-230Abstract Full Text Full Text PDF PubMed Google Scholar, 12Nakamura M. Kondo S. Sugai M. Nazarea M. Imamura S. Honjo T. Int. Immunol. 1996; 8: 193-201Crossref PubMed Scopus (159) Google Scholar). Using CH12F3-2 cells, we have shown that CRS breakpoints are distributed not only within typical repetitive sequences (designated S region) but also in its flanking regions (11Lee C.G. Kondo S. Honjo T. Curr. Biol. 1998; 8: 227-230Abstract Full Text Full Text PDF PubMed Google Scholar). However, the break points were rarely found in the I and C exons, which are separated by the S region, i.e. the intron of germ-line transcripts. Because accumulating evidence indicates that transcription from I to C exon and splicing of the transcripts are essential to CSR (13Hein K. Lorenz M. Siebenkotten B. Petry K. Christine R. Radbruch A. J. Exp. Med. 1998; 188: 2369-2374Crossref PubMed Scopus (124) Google Scholar, 14Lorenz M. Jung S. Radbruch A. Science. 1995; 267: 1825-1828Crossref PubMed Scopus (214) Google Scholar), it is possible that the transcripts are involved directly or indirectly in CSR. We have thus proposed that a complex structure of DNA and RNA, but not S region sequence per se, is recognized for initiation of CSR (11Lee C.G. Kondo S. Honjo T. Curr. Biol. 1998; 8: 227-230Abstract Full Text Full Text PDF PubMed Google Scholar). This idea gained further support with the finding that CSR can take place efficiently even when the Sα region was replaced by the Sε or Sγ1 region in minichromosomal constructs introduced in CH12F3-2 cells upon cytokine stimulation (10Kinoshita K. Tashiro J. Tomita S. Lee Chung-Gi Honjo T. Immunity. 1998; 9: 349-358Abstract Full Text Full Text PDF Scopus (67) Google Scholar).Another type of genetic regulation, RNA-editing, is widely used as a means to create new functional genes from the restricted genome in plants and protozoa (15Scott J. Cell. 1995; 81: 833-836Abstract Full Text PDF PubMed Scopus (101) Google Scholar, 16Simpson L. Thiemann O.H. Cell. 1995; 81: 837-840Abstract Full Text PDF PubMed Scopus (71) Google Scholar). An increasing number of mammalian mRNAs are also known to be edited, including apolipoprotein B (apoB) mRNA, glutamate receptor mRNA, Wilms tumor-1 mRNA, α-galactosidase mRNA, neurofibromatosis type-1 mRNA, and tRNAAsp (17Smith H.C. Sowden M.P. Trends Genet. 1996; 12: 418-424Abstract Full Text PDF PubMed Scopus (50) Google Scholar). Although most of their molecular mechanisms are yet to be elucidated, that of apoB mRNA editing by APOBEC-1(18, 19) is extensively documented. ApoB mRNA editing involves a site-specific C to U deamination of the first base of a CAA codon, encoding glutamine at residue 2153 in apoB100, and produces a UAA in-frame stop codon in apoB48 mRNA (20Navaratnam N. Bhattacharya S. Fujino T. Patel D. Jarmuz A.L. Scott J. Cell. 1995; 81: 187-195Abstract Full Text PDF PubMed Scopus (157) Google Scholar). ApoB100 and apoB48 are translation products of the unedited and edited apoB mRNAs, respectively, and these proteins have completely different physiological functions (21Innerarity T.L. Boren J. Yamanaka S. Olofsson S.O. J. Biol. Chem. 1996; 271: 2353-2356Abstract Full Text Full Text PDF PubMed Scopus (123) Google Scholar). APOBEC-1 requires an auxiliary factor(s) for site-specific RNA editing of apoB mRNA (18Teng B. Burant C.F. Davidson N.O. Science. 1993; 260: 1816-1819Crossref PubMed Scopus (491) Google Scholar, 19Navaratnam N. Bhattacharya S. Patel D. T. F. Davidson N.O. Scott J. J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar). APOBEC-1 cytidine deaminase activity on a and affinity to AU-rich RNA N. Bhattacharya S. Patel D. T. F. Davidson N.O. Scott J. J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar, N. Bhattacharya S. Fujino T. Patel D. Jarmuz A.L. Scott J. Cell. 1995; 81: 187-195Abstract Full Text PDF PubMed Scopus (157) Google Scholar, S. Davidson N.O. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Davidson N.O. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). and activity of the auxiliary are found not only in that apoB mRNA editing but also in that have of APOBEC-1 or apoB mRNA (18Teng B. Burant C.F. Davidson N.O. Science. 1993; 260: 1816-1819Crossref PubMed Scopus (491) Google Scholar, 19Navaratnam N. Bhattacharya S. Patel D. T. F. Davidson N.O. Scott J. J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar, S. T.L. J. Biol. Chem. Full Text PDF PubMed Google Scholar). expression of the auxiliary in the of APOBEC-1 that the auxiliary may be involved in more functions or editing of However, is known the or activity of these this we of cDNA encoding a (AID) that is to the apoB RNA-editing enzyme, The restricted expression and of AID within B cells in that AID may play a role in genetic events in dissect the molecular mechanism of CSR, we cDNA from and CH12F3-2 cells on the that of as switch are required for CSR. In support of it was that the of DNA in CH12F3-2 cells and the for protein for CSR to take novel genes thus we have which is induced in B cells upon AID the for cytidine deaminase and deamination of cytidine in vitro The of and of zinc on activity that the deamination process may be to that of including revealed that AID is to the RNA-editing deaminase than despite the that AID RNA editing activity on an apoB RNA that and in APOBEC-1 are essential for RNA (17Smith H.C. Sowden M.P. Trends Genet. 1996; 12: 418-424Abstract Full Text PDF PubMed Scopus (50) Google Scholar, N. Bhattacharya S. Fujino T. Patel D. Jarmuz A.L. Scott J. Cell. 1995; 81: 187-195Abstract Full Text PDF PubMed Scopus (157) Google Scholar, S. Davidson N.O. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Davidson N.O. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). These were to be in the AID structure However, as AID was not found to apoB RNA on the deaminase revealed its which with the structure of The deaminase family can be two in the of the N. Fujino T. J. Jarmuz A. A. N. A. Bhattacharya S. C. Scott J. J. Biol. 1998; PubMed Scopus (124) Google Scholar). cytidine deaminase and APOBEC-1 have a in the C which is required to a the and AID a C which is than but to the of APOBEC-1 that AID to the cytidine deaminase The of AID to APOBEC-1 that AID may be a novel RNA-editing deaminase induced in B cells, it to be AID a or a with the auxiliary used by of this of the auxiliary mRNA was induced in CH12F3-2 cells within after cytokine stimulation The of AID mRNAs and the of CSR in cells thus AID mRNA expression was induced in splenic B cells after in with and which naive B cells to CSR AID mRNAs were also in splenic B in when were immunized with the experiments and in situ hybridization revealed that AID mRNA was in B cells, which are to somatic hypermutation and CSR. In of the that not support CSR, including and were found to AID mRNA not Taken together, these that AID mRNA is a B gene induced upon stimulation. restricted expression of the AID gene in B cells with the of AID and CSR suggest its role in the of RNA-editing activity on to that AID may in to as somatic hypermutation and CSR. is of that the of CSR in CH12F3-2 cells is to when cells were in the of not The physiological of AID is by gene and The germinal center (GC) 1The abbreviations used are: GC, germinal center; CSR, class switch recombination; apoB, apolipoprotein B; APOBEC-1, apoB mRNAediting enzyme, catalytic polypeptide 1; CD40L, CD40 ligand; GST, glutathione S-transferase; THU, tetrahydrouridine; LPS, lipopolysaccharide; RBC, red blood cells; SRBC, sheep RBC; GAPDH, glyceraldehydehyde-3-phosphate dehydrogenase; CHX, cycloheximide; IL, interleukin; TGF, transforming growth factor; RT-PCR, reverse transcription-polymerase chain reaction; kb, kilobase(s).1The abbreviations used are: GC, germinal center; CSR, class switch recombination; apoB, apolipoprotein B; APOBEC-1, apoB mRNAediting enzyme, catalytic polypeptide 1; CD40L, CD40 ligand; GST, glutathione S-transferase; THU, tetrahydrouridine; LPS, lipopolysaccharide; RBC, red blood cells; SRBC, sheep RBC; GAPDH, glyceraldehydehyde-3-phosphate dehydrogenase; CHX, cycloheximide; IL, interleukin; TGF, transforming growth factor; RT-PCR, reverse transcription-polymerase chain reaction; kb, kilobase(s). constitutes a highly specialized microenvironment required for the final maturation step of naive B cells toward antigen-specific memory cells or long-lived plasma cells (1Smith K.G. Light A. Nossal G.J. Tarlinton D.M. EMBO. J. 1997; 16: 2996-3006Crossref PubMed Scopus (333) Google Scholar, 2George J. Claflin L. Semin. Immunol. 1992; 4: 11-17PubMed Google Scholar). Two prominent alterations of immunoglobulin gene information are known to occur in this microenvironment (3Jacob J. Kassir R. Kelsoe G. J. Exp. Med. 1991; 173: 1165-1175Crossref PubMed Scopus (591) Google Scholar, 4Kraal G. Weissman I.L. Butcher E.C. Adv. Exp. Med. Biol. 1985; 186: 145-151PubMed Google Scholar, 5Berek C. Berger A. Apel M. Cell. 1991; 67: 1121-1129Abstract Full Text PDF PubMed Scopus (748) Google Scholar). First, accumulation of massive point mutations in the variable region exon, a process refer to as somatic hypermutation (6Neuberger M.S. Milstein C. Curr. Opin. Immunol. 1995; 7: 248-254Crossref PubMed Scopus (249) Google Scholar), gives rise to affinity maturation of antibody in association with selection of B cells expressing high affinity immunoglobulins on their surface (7Sablitzky F. Wildner G. Rajewsky K. EMBO J. 1985; 4: 345-350Crossref PubMed Scopus (108) Google Scholar, 8Kocks C. Rajewsky K. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 8206-8210Crossref PubMed Scopus (147) Google Scholar). Second, class switch recombination (CSR) replaces the exons encoding the heavy chain constant region (9Lorenz M. Radbruch A. Curr. Top. Microbiol. Immunol. 1996; 217: 151-169PubMed Google Scholar), which determines effector functions of the antibody including complement fixation. These two alterations of immunoglobulin gene information are critical for accounting for an effective humoral response to harmful microbes. The molecular mechanisms for these genetic events remain to be elucidated despite intensive dissect the molecular mechanism of class switching, we have isolated a murine B lymphoma clone CH12F3-2 in which CSR from IgM to IgA begins to occur within a few hours after stimulation with IL-4, TGF-β, and CD40L, giving rise to more than 80% IgA+ cells (10Kinoshita K. Tashiro J. Tomita S. Lee Chung-Gi Honjo T. Immunity. 1998; 9: 349-358Abstract Full Text Full Text PDF Scopus (67) Google Scholar, 11Lee C.G. Kondo S. Honjo T. Curr. Biol. 1998; 8: 227-230Abstract Full Text Full Text PDF PubMed Google Scholar, 12Nakamura M. Kondo S. Sugai M. Nazarea M. Imamura S. Honjo T. Int. Immunol. 1996; 8: 193-201Crossref PubMed Scopus (159) Google Scholar). Using CH12F3-2 cells, we have shown that CRS breakpoints are distributed not only within typical repetitive sequences (designated S region) but also in its flanking regions (11Lee C.G. Kondo S. Honjo T. Curr. Biol. 1998; 8: 227-230Abstract Full Text Full Text PDF PubMed Google Scholar). However, the break points were rarely found in the I and C exons, which are separated by the S region, i.e. the intron of germ-line transcripts. Because accumulating evidence indicates that transcription from I to C exon and splicing of the transcripts are essential to CSR (13Hein K. Lorenz M. Siebenkotten B. Petry K. Christine R. Radbruch A. J. Exp. Med. 1998; 188: 2369-2374Crossref PubMed Scopus (124) Google Scholar, 14Lorenz M. Jung S. Radbruch A. Science. 1995; 267: 1825-1828Crossref PubMed Scopus (214) Google Scholar), it is possible that the transcripts are involved directly or indirectly in CSR. We have thus proposed that a complex structure of DNA and RNA, but not S region sequence per se, is recognized for initiation of CSR (11Lee C.G. Kondo S. Honjo T. Curr. Biol. 1998; 8: 227-230Abstract Full Text Full Text PDF PubMed Google Scholar). This idea gained further support with the finding that CSR can take place efficiently even when the Sα region was replaced by the Sε or Sγ1 region in minichromosomal constructs introduced in CH12F3-2 cells upon cytokine stimulation (10Kinoshita K. Tashiro J. Tomita S. Lee Chung-Gi Honjo T. Immunity. 1998; 9: 349-358Abstract Full Text Full Text PDF Scopus (67) Google Scholar). type of genetic regulation, RNA-editing, is widely used as a means to create new functional genes from the restricted genome in plants and protozoa (15Scott J. Cell. 1995; 81: 833-836Abstract Full Text PDF PubMed Scopus (101) Google Scholar, 16Simpson L. Thiemann O.H. Cell. 1995; 81: 837-840Abstract Full Text PDF PubMed Scopus (71) Google Scholar). An increasing number of mammalian mRNAs are also known to be edited, including apolipoprotein B (apoB) mRNA, glutamate receptor mRNA, Wilms tumor-1 mRNA, α-galactosidase mRNA, neurofibromatosis type-1 mRNA, and tRNAAsp (17Smith H.C. Sowden M.P. Trends Genet. 1996; 12: 418-424Abstract Full Text PDF PubMed Scopus (50) Google Scholar). Although most of their molecular mechanisms are yet to be elucidated, that of apoB mRNA editing by APOBEC-1(18, 19) is extensively documented. ApoB mRNA editing involves a site-specific C to U deamination of the first base of a CAA codon, encoding glutamine at residue 2153 in apoB100, and produces a UAA in-frame stop codon in apoB48 mRNA (20Navaratnam N. Bhattacharya S. Fujino T. Patel D. Jarmuz A.L. Scott J. Cell. 1995; 81: 187-195Abstract Full Text PDF PubMed Scopus (157) Google Scholar). ApoB100 and apoB48 are translation products of the unedited and edited apoB mRNAs, respectively, and these proteins have completely different physiological functions (21Innerarity T.L. Boren J. Yamanaka S. Olofsson S.O. J. Biol. Chem. 1996; 271: 2353-2356Abstract Full Text Full Text PDF PubMed Scopus (123) Google Scholar). APOBEC-1 requires an auxiliary factor(s) for site-specific RNA editing of apoB mRNA (18Teng B. Burant C.F. Davidson N.O. Science. 1993; 260: 1816-1819Crossref PubMed Scopus (491) Google Scholar, 19Navaratnam N. Bhattacharya S. Patel D. T. F. Davidson N.O. Scott J. J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar). APOBEC-1 cytidine deaminase activity on a and affinity to AU-rich RNA N. Bhattacharya S. Patel D. T. F. Davidson N.O. Scott J. J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar, N. Bhattacharya S. Fujino T. Patel D. Jarmuz A.L. Scott J. Cell. 1995; 81: 187-195Abstract Full Text PDF PubMed Scopus (157) Google Scholar, S. Davidson N.O. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Davidson N.O. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). and activity of the auxiliary are found not only in that apoB mRNA editing but also in that have of APOBEC-1 or apoB mRNA (18Teng B. Burant C.F. Davidson N.O. Science. 1993; 260: 1816-1819Crossref PubMed Scopus (491) Google Scholar, 19Navaratnam N. Bhattacharya S. Patel D. T. F. Davidson N.O. Scott J. J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar, S. T.L. J. Biol. Chem. Full Text PDF PubMed Google Scholar). expression of the auxiliary in the of APOBEC-1 that the auxiliary may be involved in more functions or editing of However, is known the or activity of these In this we of cDNA encoding a (AID) that is to the apoB RNA-editing enzyme, The restricted expression and of AID within B cells in that AID may play a role in genetic events in dissect the molecular mechanism of CSR, we cDNA from and CH12F3-2 cells on the that of as switch are required for CSR. In support of it was that the of DNA in CH12F3-2 cells and the for protein for CSR to take novel genes thus we have which is induced in B cells upon AID the for cytidine deaminase and deamination of cytidine in vitro The of and of zinc on activity that the deamination process may be to that of including revealed that AID is to the RNA-editing deaminase than despite the that AID RNA editing activity on an apoB RNA that and in APOBEC-1 are essential for RNA (17Smith H.C. Sowden M.P. Trends Genet. 1996; 12: 418-424Abstract Full Text PDF PubMed Scopus (50) Google Scholar, N. Bhattacharya S. Fujino T. Patel D. Jarmuz A.L. Scott J. Cell. 1995; 81: 187-195Abstract Full Text PDF PubMed Scopus (157) Google Scholar, S. Davidson N.O. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Davidson N.O. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). These were to be in the AID structure However, as AID was not found to apoB RNA on the deaminase revealed its which with the structure of The deaminase family can be two in the of the N. Fujino T. J. Jarmuz A. A. N. A. Bhattacharya S. C. Scott J. J. Biol. 1998; PubMed Scopus (124) Google Scholar). cytidine deaminase and APOBEC-1 have a in the C which is required to a the and AID a C which is than but to the of APOBEC-1 that AID to the cytidine deaminase The of AID to APOBEC-1 that AID may be a novel RNA-editing deaminase induced in B cells, it to be AID a or a with the auxiliary used by of this of the auxiliary mRNA was induced in CH12F3-2 cells within after cytokine stimulation The of AID mRNAs and the of CSR in cells thus AID mRNA expression was induced in splenic B cells after in with and which naive B cells to CSR AID mRNAs were also in splenic B in when were immunized with the experiments and in situ hybridization revealed that AID mRNA was in B cells, which are to somatic hypermutation and CSR. In of the that not support CSR, including and were found to AID mRNA not Taken together, these that AID mRNA is a B gene induced upon stimulation. restricted expression of the AID gene in B cells with the of AID and CSR suggest its role in the of RNA-editing activity on to that AID may in to as somatic hypermutation and CSR. is of that the of CSR in CH12F3-2 cells is to when cells were in the of not The physiological of AID is by gene and dissect the molecular mechanism of CSR, we cDNA from and CH12F3-2 cells on the that of as switch are required for CSR. In support of it was that the of DNA in CH12F3-2 cells and the for protein for CSR to take place. novel genes thus we have which is induced in B cells upon AID the for cytidine deaminase and deamination of cytidine in vitro The of and of zinc on activity that the deamination process may be to that of including revealed that AID is to the RNA-editing deaminase than despite the that AID RNA editing activity on an apoB RNA that and in APOBEC-1 are essential for RNA (17Smith H.C. Sowden M.P. Trends Genet. 1996; 12: 418-424Abstract Full Text PDF PubMed Scopus (50) Google Scholar, N. Bhattacharya S. Fujino T. Patel D. Jarmuz A.L. Scott J. Cell. 1995; 81: 187-195Abstract Full Text PDF PubMed Scopus (157) Google Scholar, S. Davidson N.O. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Davidson N.O. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). These were to be in the AID structure However, as AID was not found to apoB RNA on the deaminase revealed its which with the structure of The deaminase family can be two in the of the N. Fujino T. J. Jarmuz A. A. N. A. Bhattacharya S. C. Scott J. J. Biol. 1998; PubMed Scopus (124) Google Scholar). cytidine deaminase and APOBEC-1 have a in the C which is required to a the and AID a C which is than but to the of APOBEC-1 that AID to the cytidine deaminase The of AID to APOBEC-1 that AID may be a novel RNA-editing deaminase induced in B cells, it to be AID a or a with the auxiliary used by of this of the auxiliary AID mRNA was induced in CH12F3-2 cells within after cytokine stimulation The of AID mRNAs and the of CSR in cells thus AID mRNA expression was induced in splenic B cells after in with and which naive B cells to CSR AID mRNAs were also in splenic B in when were immunized with the experiments and in situ hybridization revealed that AID mRNA was in B cells, which are to somatic hypermutation and CSR. In of the that not support CSR, including and were found to AID mRNA not Taken together, these that AID mRNA is a B gene induced upon stimulation. restricted expression of the AID gene in B cells with the of AID and CSR suggest its role in the of RNA-editing activity on to that AID may in to as somatic hypermutation and CSR. is of that the of CSR in CH12F3-2 cells is to when cells were in the of not The physiological of AID is by gene and We S. and K. for and We also M. and T. for their and and T. for