Complete DNA sequence of the mitochondrial genome of Cepaea nemoralis (Gastropoda: Pulmonata).

The nucleotide sequence of a mitochondrial genome of the pulmonate gastropod mollusc Cepaea nemoralis has been determined. Contained within the 14,100 basepairs (bp) are the two ribosomal RNA genes and 13 protein coding genes typical of metazoan mitochondrial genomes. The Cepaea mtDNA does contain a gene for ATPase subunit 8, like the clausiliid pulmonate, Albinaria, and the chiton, Katharina, but unlike the bivalve mollusc, Mytilus. The mitochondrial genetic code of Cepaea is proposed to be the same as that of Mytilus, Katharina, and Drosophila. Only 14 putative tRNA genes are presented, although there is sufficient unassigned sequence to encode the remainder of the expected total of 22 tRNA genes. These 14 tRNA genes are a mixture of standard cloverleaf structures and nonstandard structures containing TV replacement loops as seen in nematode and mosquito mitochondrial genomes. If the eight unidentified tRNA genes are indeed present, very little unassigned sequence would remain to serve as a control region. Genes are transcribed from both strands of the molecule. Base composition is the least biased for any reported animal mitochondrial genome and is also very little skewed between strands using measures independent of base composition. The Cepaea mitochondrial gene order is quite unlike that of any other reported metazoan mtDNA, with the exception of the recently reported partial sequences of Albinaria. No gene boundaries are shared among all the reported molluscan taxa, demonstrating a complete lack of conservation of mitochondrial gene order across the phylum Mollusca.