Polymorphism and evolution in the constant region

Authors: Sondra M Kamper Churchill E McKinney

Publish Date: 2002/02/07

Volume: 53, Issue: 12, Pages: 1047-1054

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Abstract

Sequence PCR and Southern data are presented as evidence that as in mammals two gene loci encode C regions of the TCR β chain in the bicolor damselfish Stegastes partitus The loci are distinguished by an insertion of ten amino acids in the c–d loop at one locus and by a high interlocus divergence of the third intron and fourth exon sequences Unlike their mammalian counterparts the damselfish TCRBC genes encode highly polymorphic regions None of the eight complete cDNA or four partial genomic DNA sequences presented from a single animal are identical and three of the four animals examined are heterozygous at both loci suggesting high heterozygosity in the damselfish population Coding regions of the eight cDNA clones differ by up to 12 at the DNA level and 23 at the amino acid level Polymorphism is concentrated primarily in the less evolutionarily conserved regions suggesting that this variation may be selectively neutral However a comparison of the variation between synonymous and nonsynonymous sites suggests that at least a portion of the observed variation results from selection As in mammals a gradient of sequence homogenization between the two loci is observed Data presented here suggest that both interlocus homogenization and the sharing of polymorphic segments are likely achieved by partial gene conversion

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