Molecular Biology and Evolution, Vol 14, 1316-1325, Copyright © 1997 by Society for Molecular Biology and Evolution
T Luque, G Marfany and R Gonzalez-Duarte
Retrosequences, genes, and pseudogenes originated by retrotranscription are
frequent components of vertebrate genomes, but they have only occasionally
been described in invertebrates. In Drosophila, very few retrosequences
have been reported, among them those of alcohol dehydrogenase (Adh) and
phosphoglyceromutase (Pglym). Although 52 Adh gene sequences are available
for comparison, Adh retrosequences have been described only in the sibling
species D. teissieri and D. yakuba (melanogaster subgroup) and in D.
subobscura (obscura subgroup). Here, we report the presence of Adh
retrosequences in two closely related species of D. subobscura: D.
madeirensis and D. guanche. Extensive sequence comparisons with their
functional paralogs suggest separate retrotranscriptional events: one in
the melanogaster subgroup in the ancestor of D. teissieri and D. yakuba,
and the other in the obscura subgroup before the radiation of the lineages
leading to D. subobscura, D. madeirensis, and D. guanche. In the former,
the Adh retrotranscript originated a new expressed gene, named jingwei.
However, in the obscura Adh retrosequences, retention of codon bias and
higher Ks than Ka values, both distinctive evolutionary features supporting
functionality, have to be considered together with a frameshift, premature
stop codons, and other nucleotide substitutions, which, added to the lack
of the original promoter elements, suggest that they are pseudogenes. At
least two different Adh retrosequences have been characterized in each of
the obscura species, and their phylogenetic analysis indicates that
paralogs and their flanking genomic regions share a higher degree of
similarity than orthologous sequences. Two alternative hypotheses could
explain this current organization and structure: either a multiplication
event occurred independently in each species, or gene conversion events
should be invoked after a single duplication in the species ancestor. The
significance of retrotranscriptional events in the evolution of
invertebrate genomes is discussed.
ORIGINAL ARTICLE
Characterization and molecular analysis of Adh retrosequences in species of the Drosophila obscura group
Department de Genetica, Facultat de Biologia, Universitat de Barcelona, Spain.
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