Evolution of the mouse beta-globin genes: a recent gene conversion in the Hbbs haplotype |
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Authors: | Erhart MA; Simons KS; Weaver S |
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Institution: | Department of Biological Sciences, University of Illinois, Chicago 60680. |
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Abstract: | We have determined the complete nucleotide sequence of the two nonallelic
adult beta-globin genes of the C57BL/10 mouse. These genes, designated beta
s and beta t, show a sequence similarity of 99.6% over the region bordered
by the translational start and stop codons. Both beta s and beta t encode
functional polypeptide chains that are identical. A comparison of the
C57BL/10 beta-globin haplotype, Hbbs, with that of the BALB/c mouse, Hbbd,
suggests that the two haplotypes have distinct evolutionary histories. The
two adult beta-globin genes of the Hbbd haplotype, beta dmaj and beta dmin,
are 16% divergent at the nucleotide level and encode distinct polypeptides
that are synthesized in differing amounts. Our analysis indicates that a
gene correction mechanism has been operating on the Hbbs chromosome to keep
beta s and beta t evolving in concert, whereas on the Hbbd chromosome, beta
dmin has diverged considerably from beta dmaj. We suggest that gene
conversion is responsible for the maintained similarity of the Hbbs genes.
Furthermore, we attribute the divergence of the Hbbd genes in part to the
absence of a region of simple-sequence DNA within the large intervening
sequence of beta dmin. We propose that this region of DNA plays a role in
facilitating gene conversion. The deletion of this area in beta dmin
introduced a block of nonhomology between the beta dmaj-beta dmin gene pair
and thus may have inhibited further gene correction within the Hbbd
haplotype.
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