Gene rearrangements in snake mitochondrial genomes: highly concerted evolution of control-region-like sequences duplicated and inserted into a tRNA gene cluster |
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Authors: | Kumazawa Y; Ota H; Nishida M; Ozawa T |
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Institution: | Department of Earth and Planetary Sciences, Nagoya University, Japan. h44858a@nucc.cc.nagoya-u.ac.jp |
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Abstract: | Mitochondrial DNA (mtDNA) regions corresponding to two major tRNA gene
clusters were amplified and sequenced for the Japanese pit viper, himehabu.
In one of these clusters, which in most vertebrates characterized to date
contains three tightly connected genes for tRNA(Ile), and tRNA(Gln), and
tRNA(Met), a sequence of approximately 1.3 kb was found to be inserted
between the genes for tRNA(Ile) and tRNA(Gln). The insert consists of a
control-region-like sequence possessing some conserved sequence blocks, and
short flanking sequences which may be folded into tRNA(Pro), tRNA(Phe), and
tRNA(Leu) genes. Several other snakes belonging to different families were
also found to possess a control-region-like sequence and tRNA(Leu) gene
between the tRNA(Ile)and tRNA(Gln) genes. We also sequenced a region
surrounded by genes for cytochrome b and 12S rRNA, where the control region
and genes for tRNA(Pro) and tRNA(Phe) are normally located in the mtDNAs of
most vertebrates. In this region of three examined snakes, a
control-region- like sequence exists that is almost completely identical to
the one found between the tRNA(Ile) and tRNA(Gln) genes. The mtDNAs of
these snakes thus possess two nearly identical control-region-like
sequences which are otherwise divergent to a large extent between the
species. These results suggest that the duplicate state of the
control-region- like sequences has long persisted in snake mtDNAs, possibly
since the original insertion of the control-region-like sequence and
tRNA(Leu) gene into the tRNA gene cluster, which occurred in the early
stage of the divergence of snakes. It is also suggested that the duplicated
control-region-like sequences at two distant locations of mtDNA have
evolved concertedly by a mechanism such as frequent gene conversion. The
secondary structures of the determined tRNA genes point to the operation of
simplification pressure on the T psi C arm of snake mitochondrial tRNAs.
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