Molecular Biology and Evolution, Vol 15, 236-250, Copyright © 1998 by Society for Molecular Biology and Evolution
SV Edwards, J Gasper and M March
To further our understanding of the evolution of avian Mhc genes at the
genomic level, we screened a cosmid library made from a red-winged
blackbird (Agelaius phoeniceus) with a blackbird cDNA probe and subcloned
from one of the Mhc-containing cosmids a gene which we designate Agph-DAB1.
The structure of the gene is similar to that found for chicken class II B
genes, except that the introns are surprisingly large, ranging from 98 to
over 600 bp, making this the longest avian class II B gene to date. Using
primers targeted toward the introns flanking the peptide-binding region
(PBR), we amplified the entirety of the second exon and determined
nucleotide sequences of 41 PCR products from eight individual blackbirds.
The 10 sequence types found, among which were two probable pseudogene
sequences, exhibit the classic hallmarks for evolution of PBRs, namely, an
excess of nonsynonymous over synonymous substitutions and evidence of gene
conversion events in polymorphic subdomains. Despite these patterns and our
use of intron primers, the distribution of sequences among individuals
suggests that more than one locus was amplified in most individuals, and
the bushlike tree of sequences provides little information as to
locus-specific clusters. These results imply a complex history of gene
conversion, recent duplication, or possibly, concerted evolution among
multiple loci, although Agph-DAB1, the first genomic Mhc sequence from a
bird other than chicken, provides important clues in the quest for locus-
specific Mhc primers in birds.
ORIGINAL ARTICLE
Genomics and polymorphism of Agph-DAB1, an Mhc class II B gene in red- winged blackbirds (Agelaius phoeniceus)
Department of Zoology, University of Washington, Seattle 98195, USA. edwards@zoology.washington.edu
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