Interrelatedness of 5S RNA sequences investigated by correspondence analysis

Electron microscopy may reveal structure of docosahexaenoic acid-rich oil within Schizochytrium sp

Schizochytrium sp. is an algae-like microorganism utilized for commercial production of docosahexaenoic acid (DHA)-rich oil and dried microalgae for use as a source of DHA in foods, feeds, and nutritional supplements. Electron microscopic analysis of whole cells of Schizochytrium sp. employing sample preparation by high-pressure freeze substitution suggests the presence of secondary and tertiary semicrystalline structures of triacylglycerols within the oil bodies in Schizochytrium sp. A fine secondary structure consisting of alternating light- and dark-staining bands was observed inside the oil bodies. Dark bands were 29 +/- 1 A in width, and light bands were 22 +/- 1 A in width. The tertiary (three-dimensional) structure may be a multilayered ribbon-like structure which appears coiled and interlaced within the oil body. In freeze-fracture photomicrographs, Schizochytrium oil bodies exhibited fracture planes with terraces averaging 52 +/- 7 A in height which could correspond to the combined width of two halves of two light bands and one dark band observed in the high-pressure freeze substitution photomicrographs. The results suggest that triacylglycerols within Schizochytrium sp. oil bodies may be organized in a triple chain-length structure. High-pressure freeze substitution electron micrographs of two other highly unsaturated oil-producing species of microalgae, Thraustochytrium sp. and Isochrysis galbana, also revealed this fine structure, whereas microalgae containing a higher proportion of saturated oil did not. The results suggest that the staining pattern is not an artifact of preparation and that the triple chain-length conformation of triacylglycerols in Schizochytrium sp. oil bodies may be caused by the unique fatty acid composition of the triacylglycerols.

Fusion of a free left Alu monomer and a free right Alu monomer at the origin of the Alu family in the primate genomes

In the primate genome, a typical Alu element corresponds to a dimeric structure composed of two different but related monomeric sequences arranged in tandem. However, the analysis of primate sequences found in GenBank reveals the presence of free left and free right Alu elements. Here, we report the statistical study of those monomeric elements. We found that only a small fraction of them results from a deletion of a dimeric Alu sequence. The majority derives from the amplification of monomeric progenitor sequences and constitutes two families of monomeric elements: a family of free left Alu monomers that is composed of two subfamilies and a small family of free right Alu monomers. Both families predated the dimeric Alu elements, and a phylogenetic analysis strongly suggests that the first progenitor of the dimeric Alu family arose through the fusion of a free left monomer with a free right monomer.

Successive waves of fixation of B1 variants in rodent lineage history

A new method of analyzing phylogenetic relations among members of sequence family (Quentin 1988) discriminates at least six possible B1 subfamilies in the mouse genome. Several additional and independent observations suggest that these groupings have evolutionary significance, and that successive waves of fixation of new variants occur during rodent lineage history. We have reason to believe that, in a genome, the founder sequences of different families of retroposons are in competition with regard to the amplification/fixation process.