Molecular Biology and Evolution, Vol 14, 666-673, Copyright © 1997 by Society for Molecular Biology and Evolution
Y Tan and MA Riley
To explore the molecular mechanisms behind the diversification of colicin
gene clusters, we examined DNA sequence polymorphism for the colicin gene
clusters of 14 colicin E2 (ColE2) plasmids obtained from natural isolates
of Escherichia coli. Two types of ColE2 plasmids are revealed, with type II
gene clusters generated by recombination between type I ColE2 and ColE7
gene clusters. The levels and patterns of DNA polymorphism are different
between the two types. Type I polymorphism is distributed evenly along the
gene cluster, while type II accumulates polymorphism at an elevated rate in
the 5' end of the colicin gene. These differences may be explained by
recombinational origins of type II gene clusters. The pattern of divergence
between the ColE2 gene cluster and its close relative ColE9 is not
correlated with the pattern of polymorphism within ColE2, suggesting that
this gene cluster is not evolving in a neutral fashion. A statistical test
confirms significant departures from the predictions of neutrality. These
data lend further support to the hypothesis that colicin gene clusters may
evolve under the influence of nonneutral forces.
ORIGINAL ARTICLE
Nucleotide polymorphism in colicin E2 gene clusters: evidence for nonneutral evolution
Department of Biology, Yale University, New Haven, Connecticut 06520- 8104, USA.
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