Evolution of the interleukin-1 gene family in mammals.
The phylogeny of interleukin-1 family genes shows that human interleukin-1 alpha (IL-1 alpha) is more closely related to IL-1 alpha of the bovine than to IL-1 alpha of the mouse, whereas human interleukin-1 beta (IL-1 beta) is more closely related to IL-1 beta of the mouse than to IL-1 beta of the bovine. The IL-1 receptor antagonist (IL-1ra) shows homology to the C-terminal region of both IL-1 alpha and IL-1 beta. In the C-terminal region, the IL-1 alpha genes of human and mouse have diverged more from each other at nonsynonymous sites than have either IL-1 beta or IL-1ra; because the same pattern is not seen at synonymous sites, it must be due not to a difference in mutation rate but rather to a greater degree of functional constraint on this region in the IL-1 beta and IL-1ra proteins than in the IL-1 alpha protein. But synonymous sites in IL-1 beta of mouse have evolved more rapidly than in IL-1 beta of human, indicating a higher rate of mutation in the former gene. In the N-terminal region of the protein, nonsynonymous sites have evolved at similar rates in IL-1 alpha and IL-1 beta. The first exon of the IL-1ra gene, which encodes the leader peptide, shows evidence of homology with the first exon of IL-1 beta, which is not translated. Thus, it seems likely that IL-1ra evolved by duplication of an IL-1 beta gene and loss of expression of exons 2-4.
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Department of Biology, Mueller Laboratory, Pennsylvania State University, University Park 16802.
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D002417:Cattle; D003062:Codon / Q000235:genetics; D005091:Exons; D006801:Humans; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1 / Q000235:genetics*; D008322:Mammals / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D012795:Sialoglycoproteins / Q000235:genetics
D003062:Codon; C507763:IL1RN protein, human; C507764:Il1rn protein, mouse; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1; D012795:Sialoglycoproteins