Identification of a homolog of the Cα3′/hs3 enhancer and of an allelic variant of the 3′IgH/hs1,2 enhancer downstream the human immunoglobulin α1 gene

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Abstract
Although four regulatory elements are known downstream the mouse IgH α gene, a single enhancer homologous to hs1,2 has been thus far described downstream each human α gene (Chen, C. and Birshtein, B. K., J. Immunol. 1997. 159: 1310). We characterized a 10‐kb region downstream the human α1 gene. Two B cell‐specific regulatory elements homologous to the murine Cα3′/hs3 and hs1,2 3′ enhancers were found, which are duplicated downstream α2. The hs1,2 element is in inverted orientation by comparison with a recently reported α1 hs1,2 element: it appears as a common allelic variant carrying an internal tandem repeat insertion and its prevalence in the human population is 60%. As in the mouse, the human hs1,2 enhancer is flanked with long inverted repeats which may have promoted inversion events through homologous recombination. Although the palindromic organization of the region is maintained in human, sequence identity with rodents focuses on core enhancer elements rather than on flanking repeats. Concerted divergence of both sides of the dyad symmetry suggests that inverted repeats are not just evolutionary remnants but rather play an architectural role in the LCR function.