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Journal Article

# DNA Sequences Mediating Class Switching in α-Immunoglobulins

Mark M. Davis, Stuart K. Kim and Leroy E. Hood
Science
New Series, Vol. 209, No. 4463, Recombinant DNA (Sep. 19, 1980), pp. 1360-1365
Stable URL: http://www.jstor.org/stable/1685195
Page Count: 6

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## Abstract

Immunoglobulin class switching involves specific DNA rearrangements of the gene segments coding for heavy chain constant regions (C$_{\text{H}}$) during B lymphocyte differentiation. In two different cases of C$_{\mu}$ to C$_{\alpha}$ switching examined here (T15 and M603) and one taken from the literature (MC101), three different sites on the 5$^{\prime}$ side of C$_{\mu}$ and three different sites on the 5$^{\prime}$ side of C$_{\alpha}$ are joined together in the process of C$_{\text{H}}$ switching. The sequences surrounding the three germ-line C$_{\alpha}$ sites of recombination are highly conserved blocks of 30 nucleotides that may serve as recognition sequences for C$_{\text{H}}$ switching to the C$_{\alpha}$ gene. This putative recognition sequence is repeated 17 times in approximately 1400 nucleotides of the germ-line C$_{\alpha}$ 5$^{\prime}$ flanking sequence. The lack of homology between this C$_{\alpha}$ sequence and sequences reported for the C$_{\gamma 1}$ and C$_{\gamma 2\text{b}}$ switch sites suggests that heavy chain switching is mediated by class-specific recognition sequences and, presumably, class-specific regulatory mechanisms. In addition, it appears that in one example (MC101) C$_{\text{H}}$ switching progressed from C$_{\mu}$ to C$_{\alpha}$ to C$_{\gamma 1}$. This switching pathway may present difficulties for the simple deletional model of C$_{\text{H}}$ switching.

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