Published online
doi:10.1084/jem.20061835
The Journal of Experimental Medicine, Vol. 203, No. 13, 2919-2928
The Rockefeller University Press, 0022-1007 $30.00
© Yang et al.
Control of gene conversion and somatic hypermutation by immunoglobulin promoter and enhancer sequences
Shu Yuan Yang1,
Sebastian D. Fugmann1,2, and
David G. Schatz1,2
1 Section of Immunobiology and 2 Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06520
CORRESPONDENCE David G. Schatz: david.schatz{at}yale.edu
It is thought that gene conversion (GCV) and somatic hypermutation (SHM) of immunoglobulin (Ig) genes occur in two steps: the generation of uracils in DNA by activation-induced cytidine deaminase, followed by their subsequent repair by various DNA repair pathways to generate sequence-diversified products. It is not known how either of the two steps is targeted specifically to Ig loci. Because of the tight link between transcription and SHM, we have investigated the role of endogenous Ig light chain (IgL) transcriptional control elements in GCV/SHM in the chicken B cell line DT40. Promoter substitution experiments led to identification of a strong RNA polymerase II promoter incapable of supporting efficient GCV/SHM. This surprising finding indicates that high levels of transcription are not sufficient for robust GCV/SHM in Ig loci. Deletion of the IgL enhancer in a context in which high-level transcription was not compromised showed that the enhancer is not necessary for GCV/SHM. Our results indicate that cis-acting elements are important for Ig gene diversification, and we propose that targeting specificity is achieved through the combined action of several Ig locus elements that include the promoter.
Abbreviations used: AID, activation-induced cytidine deaminase; EF1-
, elongation factor 1-
; GCV, gene conversion; IgH, Ig heavy chain; Ig
, Ig light chain
; IgL, Ig light chain; SHM, somatic hypermutation.
S.D. Fugmann's present address is National Institute on Aging, National Institutes of Health, Baltimore, MD 21224.

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