The hyper-variable segments (323~327 bp) of the mitochondrial D-loop for 169 Carassius auratus fishes in Japan were amplified by the polymerase chain reaction and the amplified products were sequenced directly and compared. A dendrogram showing three major clusters was generated with the sequence data for 37 haplotypes at 66 polymorphic sites. One cluster (cluster I) exclusively consisted of the gengorobuna, which was regarded as an independent (sub) species. The triploid ginbuna belonged to two remaining clusters, mainly in the diploid ginbuna cluster (cluster III) and partially in the goldfish cluster (cluster II). This finding suggests that the triploid ginbuna has been derived from two different maternal lineages. The triploid ginbuna was considered to have come into existence during the last ice age on the basis of this phylogenetic data. No geographic differentiation was observed with respect to the triploid ginbuna sampled at three different localities in Japan; the Shibuta River in Kanagawa, Lake Imba in Chiba and Lake Biwa in Shiga. The phylogenetic tree also demonstrated a monophyletic relationship amongst the nigorobuna, the nagabuna and the ginbuna, sharing cluster III. The nigorobuna and nagabuna populations have most likely arisen from geographic and temporal variations within the ginbuna populations. We also discuss the evolutionary origin of the triploid in view of its paternal ancestors.

No abstract

We have determined the nucleotide sequence of the 26S large subunit (LSU) rRNA genes for two Tetrahymena species, T. thermophila and T. pyriformis. The inferred rRNA sequences are presented in their most probable secondary structures based on compensatory mutations, energy, and conservation criteria. The majority of the nucleotide changes between the two Tetrahymena LSU rRNAs and the positions of a relatively large deletion and of the processing cleavage sites resulting in the generation of the hidden break are all located within the so-called divergent domains or expansion segments. These are regions within the common core of secondary structure where expansions have taken place during the evolution of the rRNA of higher eukaryotes. The dispensable nature of some of the expansion segments has been taken as evidence of their non-functionality. However, our data show that a considerable selective constraint has operated to preserve the secondary structure of these segments. Especially in the case of the D2 and D8 segments, the presence of a considerable number of compensatory base changes suggests that the secondary structure of these regions is of functional importance. Alternatively, these expansion segments may have maintained characteristic folding patterns because only such structures are being tolerated within otherwise functionally important regions.

The complete mitochondrial (mt) genome of the gynogenetic triploid ginbuna (Carassius auratus langsdorfi, AZ3 line) has been cloned and sequenced. The genome consisted of 16,578 bp and encoded the same set of genes (13 proteins, 2 rRNAs and 22 tRNAs) in addition to a D-loop region, as described for other vertebrate mtDNAs. Comparison with other teleost mtDNAs demonstrated that the protein/rRNA-coding regions of the ginbuna were highly homologous both in length and nucleotide composition to those of the carp, indicating fairly close relationship between the triploid ginbuna and the carp. Although the size of the ginbuna D-loop was almost the same as that of the carp, the nucleotide sequence showed a moderate variation. More comprehensive sequence data of the D-loop regions will lead to the elucidation of phylogenetic relationships among Carassius auratus subspecies.

Magneto-rheological fluid dampers (MR dampers) have recently been designed to control the response of civil engineering and building structures because of their large force capacity and controllable force characteristics. To enable them to control structural responses, the dynamic characteristics of structures need to be clarified. This paper discusses the design of MR dampers with a bypass orifice mechanism and verifies their performance by means of dynamic tests and dynamic analytical models. Their dynamic characteristics are investigated experimentally to compare the performance of two different magneto-rheological fluids. One is developed by the Lord Corporation and the other is newly developed in Japan. The effectiveness and validity