Molecular Biology and Evolution, Vol 16, 1558-1567, Copyright © 1999 by Society for Molecular Biology and Evolution
AL Hughes
Two modes of evolution of repeated domains in proteins have been described:
(1) a conservative mode, whereby individual domains are conserved across
gene duplication and speciation events, and (2) a concerted mode, whereby
repeat domains become homogenized within a gene, presumably by intragenic
partial duplication and/or gene conversion. The evolution of repeated
EGF-like and fibronection-type- III-like (Fn-III) domains in the vertebrate
extracellular matrix proteins tenascin-X (TNX) and tenascin-C (TNC) was
studied by comparisons between human and mouse orthologs and between the
paralogous TNC and TNX genes. The EGF-like repeats have largely been
homogenized within each gene by concerted evolution since the duplication
of the two genes but have been conserved since the divergence of rodents
and primates. The Fn-III domains of TNC have likewise mainly evolved in a
conservative fashion since the divergence of rodents and primates. In
contrast, the Fn-III repeats of TNX fall into three distinct categories
with regard to mode of evolution: (1) The three C-terminal repeats have
been conserved since before duplication of the TNX and TNC genes. (2)
Certain other repeats have been homogenized within each gene since gene
duplication but have been conserved since the divergence of rodents and
primates. (3) Still other repeats have evolved in a concerted fashion in
rodent and primate lineages since their divergence. Remarkably, certain
introns adjacent to the exons encoding these concertedly evolving Fn-III
repeats have themselves evolved in a concerted fashion. This is the first
known example of concerted evolution of repeated introns within a protein-
coding gene.
ORIGINAL ARTICLE
Concerted evolution of exons and introns in the MHC-linked tenascin-X gene of mammals
Department of Biology, Pennsylvania State University, USA. alh13@psu.edu
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