Chitinous components of the cell wall of Fusarium oxysporum.

The cell wall of Fusarium oxysporum f. sp. lycopersici was digested with chitinase to analyze the structure of its chitinous components. In spite of a similar acetylation degree of the cell wall components to that of 25-35% acetylated chitosan, only N-acetylglucosamine disaccharide [(GlcNAc)2] was obtained from chitinase hydrolyzate of the fungal cell wall by CM-Sephadex C-25 column chromatography, while (GlcNAc)2 and several types of deacetylated chitooligosaccharides were separated from that of 25-35% acetylated chitosan. The results indicate that N-acetylglucosamine residues in the polysaccharide chains of the fungal cell wall are most likely condensed into some region, while acetylated residues are more scattered in 25-35% acetylated chitosan.     

Size at maturity of fluvial white-spotted charr, <Emphasis Type="Italic">Salvelinus leucomaenis</Emphasis>, around the Lake Biwa water system varies with habitat size

Size at maturity of fluvial white-spotted charr, Salvelinus leucomaenis, was studied in small headwater tributaries of nine rivers around the Lake Biwa water system, Japan. Threshold size at maturity in both sexes showed significant positive relationships with water discharge, indicating that smaller threshold sizes at maturity of fluvial white-spotted charr occurred in smaller habitats. These results provide a link between size at maturity and habitat size and have important implications for the management of both habitats and white-spotted charr populations.     

Genetic analysis of the DNA-dependent protein kinase reveals an inhibitory role of Ku in late S-G2 phase DNA double-strand break repair

Two major complementary double-strand break (DSB) repair pathways exist in vertebrates, homologous recombination (HR), which involves Rad54, and non-homologous end-joining, which requires the DNA-dependent protein kinase (DNA-PK). DNA-PK comprises a catalytic subunit (DNA-PKcs) and a DNA-binding Ku70 and Ku80 heterodimer. To define the activities of individual DNA-PK components in DSB repair, we targeted the DNA-PKcs gene in chicken DT40 cells. DNA-PKcs deficiency caused a DSB repair defect that was, unexpectedly, suppressed by KU70 disruption. We have shown previously that genetic ablation of Ku70 confers RAD54-dependent radioresistance on S-G(2) phase cells, when sister chromatids are available for HR repair. To test whether direct interference by Ku70 with HR might explain the Ku70(-/-)/DNA-PKcs(-/-/-) radioresistance, we monitored HR activities directly in Ku- and DNA-PKcs-deficient cells. The frequency of intrachromosomal HR induced by the I-SceI restriction enzyme was increased in the absence of Ku but not of DNA-PKcs. Significantly, abrogation of HR activity by targeting RAD54 in Ku70(-/-) or DNA-PKcs(-/-/-) cells caused extreme radiosensitivity, suggesting that the relative radioresistance seen with loss of Ku70 was because of HR-dependent repair pathways. Our findings suggest that Ku can interfere with HR-mediated DSB repair, perhaps competing with HR for DSB recognition.     

Multiple roles of vertebrate REV genes in DNA repair and recombination

In yeast, Rev1, Rev3, and Rev7 are involved in translesion synthesis over various kinds of DNA damage and spontaneous and UV-induced mutagenesis. Here, we disrupted Rev1, Rev3, and Rev7 in the chicken B-lymphocyte line DT40. REV1-/- REV3-/- REV7-/- cells showed spontaneous cell death, chromosomal instability/fragility, and hypersensitivity to various genotoxic treatments as observed in each of the single mutants. Surprisingly, the triple-knockout cells showed a suppressed level of sister chromatid exchanges (SCEs), which may reflect postreplication repair events mediated by homologous recombination, while each single mutant showed an elevated SCE level. Furthermore, REV1-/- cells as well as triple mutants showed a decreased level of immunoglobulin gene conversion, suggesting participation of Rev1 in a recombination-based pathway. The present study gives us a new insight into cooperative function of three Rev molecules and the Polzeta (Rev3-Rev7)-independent role of Rev1 in vertebrate cells.     

A Ds-insertion mutant of OSH6 (Oryza sativa Homeobox 6) exhibits outgrowth of vestigial leaf-like structures, bracts, in rice

OSH6 (Oryza sativa Homeobox6) is an ortholog of lg3 (Liguleless3) in maize. We generated a novel allele, termed OSH6-Ds, by inserting a defective Ds element into the third exon of OSH6, which resulted in a truncated OSH6 mRNA. The truncated mRNA was expressed ectopically in leaf tissues and encoded the N-terminal region of OSH6, which includes the KNOX1 and partial KNOX2 subdomains. This recessive mutant showed outgrowth of bracts or produced leaves at the basal node of the panicle. These phenotypes distinguished it from the OSH6 transgene whose ectopic expression led to a “blade to sheath transformation” phenotype at the midrib region of leaves, similar to that seen in dominant Lg3 mutants. Expression of a similar truncated OSH6 cDNA from the 35S promoter (35S::ΔOSH6) confirmed that the ectopic expression of this product was responsible for the aberrant bract development. These data suggest that OSH6-Ds interferes with a developmental mechanism involved in bract differentiation, especially at the basal nodes of panicles. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Amino acid substitutions in the s2 region enhance severe acute respiratory syndrome coronavirus infectivity in rat angiotensin-converting enzyme 2-expressing cells

To clarify the molecular basis of severe acute respiratory syndrome coronavirus (SARS-CoV) adaptation to different host species, we serially passaged SARS-CoV in rat angiotensin-converting enzyme 2 (ACE2)-expressing cells. After 15 passages, the virus (Rat-P15) came to replicate effectively in rat ACE2-expressing cells. Two amino acid substitutions in the S2 region were found on the Rat-P15 S gene. Analyses of the infectivity of the pseudotype-bearing S protein indicated that the two substitutions in the S2 region, especially the S950F substitution, were responsible for efficient infection. Therefore, virus adaptation to different host species can be induced by amino acid substitutions in the S2 region.     

Oxidation of elongation factor G inhibits the synthesis of the D1 protein of photosystem II

Oxidative stress inhibits the repair of photodamaged photosystem II (PSII). This inhibition is due initially to the suppression, by reactive oxygen species (ROS), of the synthesis de novo of proteins that are required for the repair of PSII, such as the D1 protein, at the level of translational elongation. To investigate in vitro the mechanisms whereby ROS inhibit translational elongation, we developed a translation system in vitro from the cyanobacterium Synechocystis sp. PCC 6803. The synthesis of the D1 protein in vitro was inhibited by exogenous H2O2. However, the addition of reduced forms of elongation factor G (EF-G), which is known to be particularly sensitive to oxidation, was able to reverse the inhibition of translation. By contrast, the oxidized forms of EF-G failed to restore translational activity. Furthermore, the overexpression of EF-G of Synechocystis in another cyanobacterium Synechococcus sp. PCC 7942 increased the tolerance of cells to H2O2 in terms of protein synthesis. These observations suggest that EF-G might be the primary target, within the translational machinery, of inhibition by ROS.     

Regulation of lipid metabolism by palmitoleate and eicosapentaenoic acid (EPA) in mice fed a high-fat diet

We investigated whether oral administration of palmitoleate ameliorates disorders of lipid metabolism to clarify the effects of one of the components of fish oil. Lipid levels in the liver and plasma were significantly decreased by palmitoleate and by EPA administration. These results suggest that palmitoleate, in addition to EPA, plays a role in the regulation of lipid metabolism by fish oil.     

<Emphasis Type="Italic">Oncorhynchus kawamurae</Emphasis> “Kunimasu,” a deepwater trout,discovered in Lake Saiko, 70 years after extinction in the original habitat,Lake Tazawa,Japan

Oncorhynchus kawamurae (Osteichthyes: Salmonidae) (common name “Kunimasu”), a species endemic to Lake Tazawa, Akita Prefecture, Japan, was believed to have been extinct since 1940. However, nine specimens were discovered in March and April 2010 in Lake Saiko, Yamanashi Prefecture, one of the lakes to which eyed eggs of the species were introduced in 1935. These were identified as O. kawamurae because of having 47–62 pyloric caeca, 37–43 gill-rakers, a black-colored body, and spawning at 30–40 m depth in early spring, which are unique characteristics within Oncorhynchus. Furthermore, the distinctiveness of Kunimasu from sympatric kokanee (O. nerka) was supported by microsatellite DNA data.