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Primordial Emergence of the Recombination Activating Gene 1 (RAG1): Sequence of the Complete Shark Gene Indicates Homology to Microbial Integrases
Ralph M. Bernstein, Samuel F. Schluter, Harris Bernstein and John J. Marchalonis
Proceedings of the National Academy of Sciences of the United States of America
Vol. 93, No. 18 (Sep. 3, 1996), pp. 9454-9459
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/39731
Page Count: 6
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The rearrangement of antibody and T-cell receptor gene segments is indispensable to the vertebrate immune response. All extant jawed vertebrates can rearrange these gene segments. This ability is conferred by the recombination activating genes I and II (RAG I and RAG II). To elucidate their origin and function, the cDNA encoding RAG I from a member of the most ancient class of extant gnathostomes, the Carcharhine sharks, was characterized. Homology domains identified within shark RAG I prompted sequence comparison analyses that suggested similarity of the RAG I and II genes, respectively, to the integrase family genes and integration host factor genes of the bacterial site-specific recombination system. Thus, the apparent explosive evolution (or ``big bang'') of the ancestral immune system may have been initiated by a transfer of microbial site-specific recombinases.
Proceedings of the National Academy of Sciences of the United States of America © 1996 National Academy of Sciences