Primordial emergence of the recombination activating gene 1 (RAG1): sequence of the complete shark gene indicates homology to microbial integrases.
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.
Bernstein
R M
RM
Department of Microbiology and Immunology, University of Arizona, College of Medicine, Tucson 85724, USA.
Schluter
S F
SF
Bernstein
H
H
Marchalonis
J J
JJ
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002645:Chickens; D017124:Conserved Sequence; D004254:DNA Nucleotidyltransferases / Q000235:genetics; D018076:DNA, Complementary / Q000737:chemistry; D016654:Genes, RAG-1; D006801:Humans; D019426:Integrases; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D012754:Sharks; D045567:VDJ Recombinases
D018076:DNA, Complementary; D004254:DNA Nucleotidyltransferases; D019426:Integrases; D045567:VDJ Recombinases