Molecular Biology and Evolution, Vol 16, 165-172, Copyright © 1999 by Society for Molecular Biology and Evolution
A Mange and JC Prudhomme
The cytoplasmic actin genes BmA3 and BmA4 of Bombyx mori were found
clustered in a single genomic clone in the same orientation. As a similar
clustering of the two cytoplasmic actin genes Ha3a and Ha3b also occurs in
another lepidopteran, Helicoverpa armigera, we analyzed the sequence of the
pair of genes from each species. Due to the high conservation of
cytoplasmic actins, the coding sequence of the four genes was easily
aligned, allowing the detection of similarities in noncoding exon and
intron sequences as well as in flanking sequences. All four genes exhibited
a conserved intron inserted in codon 117, an original position not
encountered in other species. It can thus be postulated that all of these
genes derived from a common ancestral gene carrying this intron after a
single event of insertion. The comparison of the four genes revealed that
the genes of B. mori and H. armigera are related in two different ways: the
coding sequence and the intron that interrupts it are more similar between
paralogous genes within each species than between orthologous genes of the
two species. In contrast, the other (noncoding) regions exhibited the
greatest similarity between a gene of one species and a gene of the other
species, defining two pairs of orthologous genes, BmA3 and HaA3a on one
hand and BmA4 and HaA3b on the other. However, in each species, the very
high similarities of the coding sequence and of the single intron that
interrupts it strongly suggest that gene conversion events have homogenized
this part of the sequence. As the divergence of the B. mori genes was
higher than that of the H. armigera genes, we postulated that the gene
conversion occurred earlier in the B. mori lineage. This leads us to
hypothesize that gene conversion could also be responsible for the original
transfer of the common intron to the second gene copy before the divergence
of the B. mori and H. armigera lineages.
ORIGINAL ARTICLE
Comparison of Bombyx mori and Helicoverpa armigera cytoplasmic actin genes provides clues to the evolution of actin genes in insects
Centre de Genetique Moleculaire et Cellulaire, Universite Claude Bernard Lyon I, Centre National de la Recherche Scientifique, Villeurbanne, France.
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