The main features of the craniate mitochondrial DNA between the ND1 and the COI genes were established in the common ancestor with the lancelet |
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Authors: | Delarbre C; Barriel V; Tillier S; Janvier P; Gachelin G |
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Institution: | Unite de Biologie Moleculaire du Gene, Institut National de la Sante et de la Recherche Medicale, Institut Pasteur, Paris, France. |
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Abstract: | We have cloned the mitochondrial DNA fragment extending from tRNA-Leu to
the cytochrome oxidase subunit 1 (COI) genes of Branchiostoma lanceolatum,
Myxine glutinosa, Lampetra fluviatilis, and Scyliorhinus caniculus and have
determined their respective gene sequences and organization. In all four
species, this region contains the ND1 and ND2 genes and the genes coding
eight tRNAs, namely, tRNA-Ile, -Gln, -Met, - Trp, -Ala, -Asn, -Cys, and
-Tyr. The gene order is the same in the hagfish, lamprey and dogfish. In
the lancelet, the location of the tRNA genes is slightly different. The
mitochondrial code of Myxine, Lampetra, and Scyliorhinus is identical to
that of vertebrates. The code used by the lancelet is the same with the
exception of AGA (a stop codon in vertebrates), which codes for glycine in
the lancelet. From the comparison of the four maps with already published
ones for other species, we propose that the main features of the craniate
mtDNA between the ND1 and COI genes were established in the common ancestor
to cephalochordates and vertebrates more than 400 MYA. The origin of
replication of the light-strand (Ori-L), usually located between the
tRNA-Asn and tRNA-Cys genes in vertebrates, was not found in the lancelet,
hagfish, or lamprey (Lampetra). In contrast, it was found in the dogfish.
Thus the position of Ori-L was established for the first time in the common
ancestor to the Chondrichthyes and Osteichthyes and remained present in all
later-emerging vertebrates.
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