Mitochondrial DNA of Hydra attenuata (Cnidaria): A sequence that includes an end of one linear molecule and the genes for l-rRNA, tRNA(f-Met), tRNA(Trp), COII, and ATPase8

The 3231-nucleotide-pair (ntp) sequence of one end of one of the two Linear mitochondrial (mt) DNA molecules of Hydra attenuata (phylum Cnidaria, clas s Hydrozoa, order Anthomedusae) has been determined. This segment contains complete genes for tRNA(f-Met) 1-rRNA, tRNA(Trp), subunit 2 of cytochrome c oxidase (COII), subunit 8 of ATP synthetase (ATPase8), and the 5' 136 ntp of ATPase6, These genes are arranged in the order given and are transcribed from the same strand of the molecule. As in two other cnidarians, the hexa corallian anthozoan Metridium senile and the octocorallian anthozoan Sarcop hyton glaucum, the mt-genetic code of H. attenuata is near standard. The on ly modification appears to be that TGA specifies tryptophan rather than ter mination. Also as in M. senile and S. glaucum, the encoded H. attenuata mt- tRNA(f-Met) has primary and secondary structural features resembling those of Escherichia coli initiator tRNA(t-Met). As the encoded mt-tRNA(Trp) cann ot be folded into a totally orthodox secondary structure, two alternative f orms are suggested. The encoded H. attenuata mt-1-rRNA is 1738 nt, which is 451 nt shorter than the M. senile mt-1-rRNA. Comparisons of secondary stru cture models of these two mt-1-rRNAs indicate that most of the size differe nce results from loss of nucleotides in the H, attenuata molecule at a mini mum of 46 locations, which includes elimination of six distinct helical ele ments.