title: Carboxy-terminal domain of AID required for its mRNA complex formation in vivo.
abstract: Activation-induced cytidine deaminase (AID) is essential for the class switch recombination (CSR) and somatic hypermutation (SHM) of Ig genes. Originally, AID was postulated to be an RNA-editing enzyme, because of its structural homology with a known RNA-editing enzyme, APOBEC1. In support of this idea, AID shares many of the properties of RNA-editing enzymes, including nucleocytoplasmic shuttling and a dependency on de novo protein synthesis. However, it has not been shown whether AID recognizes a specific mRNA and edits it to generate an enzyme involved in CSR or SHM. Here, we examined the association between AID and polyadenylated [poly(A)(+)] RNA in vivo, using UV cross-linking coupled with a poly(A) capture method that relies on biotinylated oligo(dT) and streptavidin-conjugated beads. We found that both exogenous AID expressed in transfected CH12 cells and endogenous AID expressed in BL2 cells were associated with poly(A)(+) RNA. Similar protein-poly(A)(+) RNA complexes were formed by APOBEC1 and APOBEC3G. However, the interactions of all of these cytidine deaminase family members, including AID, with poly(A)(+) RNA were indirect. This was expected for APOBEC1, which is known to act through an RNA-interacting cofactor, APOBEC1 complementation factor (ACF). In addition, the carboxy-terminal region of AID, which is essential for class switching, was also required for its interaction with poly(A)(+) RNA. These results suggest that the CSR activity of AID requires an ACF-like cofactor that specifically interacts with the carboxy-terminal domain of AID.
authors.affiliation: Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: Taichiro
authors.initials: T
authors.lastname: Nonaka
authors.forename: Tomomitsu
authors.initials: T
authors.lastname: Doi
authors.forename: Takae
authors.initials: T
authors.lastname: Toyoshima
authors.forename: Masamichi
authors.initials: M
authors.lastname: Muramatsu
authors.forename: Tasuku
authors.initials: T
authors.lastname: Honjo
authors.forename: Kazuo
authors.initials: K
authors.lastname: Kinoshita
mesh_terms: D000071479:APOBEC-1 Deaminase; D000071480:APOBEC-3G Deaminase; D001483:Base Sequence; D002460:Cell Line; D003564:Cytidine Deaminase / Q000737:chemistry / Q000378:metabolism*; D017931:DNA Primers; D006801:Humans; D017393:RNA Editing; D012333:RNA, Messenger / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D017931:DNA Primers; D012333:RNA, Messenger; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D000071479:APOBEC-1 Deaminase; C000605089:APOBEC1 protein, human; D000071480:APOBEC-3G Deaminase; C464924:APOBEC3G protein, human; D003564:Cytidine Deaminase