Structural integrity of {alpha}-helix H12 in translation initiation factor eIF5B is critical for 80S complex stability

Translation initiation factor eIF5B promotes GTP-dependent ribosomal subunit joining in the final step of the translation initiation pathway. The protein resembles a chalice with the α-helix H12 forming the stem connecting the GTP-binding domain cup to the domain IV base. Helix H12 has been proposed to function as a rigid lever arm governing domain IV movements in response to nucleotide binding and as a molecular ruler fixing the distance between domain IV and the G domain of the factor. To investigate its function, helix H12 was lengthened or shortened by one or two turns. In addition, six consecutive residues in the helix were substituted by Gly to alter the helical rigidity. Whereas the mutations had minimal impacts on the factor's binding to the ribosome and its GTP binding and hydrolysis activities, shortening the helix by six residues impaired the rate of subunit joining in vitro and both this mutation and the Gly substitution mutation lowered the yield of Met-tRNA(i)(Met) bound to 80S complexes formed in the presence of nonhydrolyzable GTP. Thus, these two mutations, which impair yeast cell growth and enhance ribosome leaky scanning in vivo, impair the rate of formation and stability of the 80S product of subunit joining. These data support the notion that helix H12 functions as a ruler connecting the GTPase center of the ribosome to the P site where Met-tRNA(i)(Met) is bound and that helix H12 rigidity is required to stabilize Met-tRNA(i)(Met) binding.     

STUDIES ON LACTATE CYTOCHROME C REDUCTASES OF YEAST WITH SPECIAL REFERENCE TO ELECTROPHORESIS ON POLYACRYLAMIDE GEL

1. Two lactate dehydrogenases, L(+)- and D(–)- lactate cytochromec reductase, were extracted from the baker's yeast after disintegrationof the cells by a FRENCH press. They are separated by electrophoresison polyacrylamide gel and their activities were compared bycolor density of formazan, the reduction product of nitrobluetetrazolium.
2. The ratio of L-lactate cytochrome c reductaseactivity to D-lactatecytochrome c reductase activity variedto a great extent, dependingon culture conditions. L-Lactatecytochrome c reductase waspredominant in resting cells; thereverse was the case withcells in early exponential stage ofthe growth.
3. When the cells in exponential stage of growthwere aerated withoutnitrogen source, there occurred an intensiveincrease of L-lactatecytochrome c reductase, accompanied bythe decrease of D-lactatecytochrome c reductase.
4. Effectsof inhibitors on the activity ratio of these two enzymeswereinvestigated. o-Phenanthroline, dinitrophenol, sodium azide,chloramphenicol, British antilewisite and antimycin A favored,in this order, the formation of L-lactate cytochrome c reductase.

(Received August 18, 1966; )     

Direct Infection of Hepatocytes by Sporozoites of Plasmodium berghei1

ABSTRACT. To identify the unknown liver cell type initially invaded by sporozoiles of mammalian malaria, young rats were inoculated intravenously with large numbers of Plasmodium berghei sporozoites obtained from infected Anopheles stephensi mosquitoes. Fine structural studies of liver specimens obtained from the rats within 2 min after inoculation demonstrated the presence of morphologically unaltered sporozoites in the cytoplasm of hepatocytes. Many sporozoites were also observed undergoing cytolysis within the lysophagosomes of Kupffer cells, as well as other phagocytic cells. These observations strongly suggest direct infection of the hepatocyte by the sporozoite.     

Can Once Neuronally Differentiated Cells of Neural Retina Be Lentoidogenic in Cell Culture?*

Cells dissociated from neural retina of 3.5-day-old chick embryos transdifferentiated extensively into lens cells under the conditions of a cell culture for 3 to 4 weeks. In early satges of cell culture by about 10 days, cultures consisted of small round cells often with cytoplasmic processes(N-cells) and flattened epithelial cells (E-cells). Only N-cells were stained with a fluorescent dye Merocyanine 540. When cells harvested from early cultures were separated into two fractions by centrifugation in Percoll gradient, the specific activity of choline acetyltransferase was much higher in the fraction consisting mainly of N-cells than in other fraction mainly of E-cells. Continuous daily observations as well as cinematographic observations of living cultures indicate that lentoid bodies were often formed in the locations where clusters of N-cells had been found in early stages of culturing. The possibility of transdifferentiation of N-cell clusters into lentoid bodies is discussed.     

First record of an Early Barremian caprinid rudist from Japan – implications for the palaeobiogeography of the Caprinidae (Bivalvia)

Abstract: Pachytraga Paquier, 1900, the stratigraphically oldest genus of caprinine caprinid rudist, was previously known from only two chronospecies from a single lineage, that is the Hauterivian P. tubiconcha Astre, 1961 and the early Aptian P. paradoxa (Pictet and Campiche, 1869). Here, a new species, Pachytraga? tanakahitoshii, is erected on the basis of isolated left valves recovered from the Osaka and Sanchu areas, south‐west Japan. This species has a moderate shell size (antero‐posterior commissural diameter c. 30 mm), and its left valve is characterized by at least one possibly autapomorphic character (narrow anterior myophore, inclined inwards), as well as a mosaic of primitive (single longitudinal carina developed on the anterior side) and derived (simple marginal canals in the antero‐dorsal valve margin) characters of Mediterranean and Middle East Tethyan Pachytraga. The Japanese Pachytraga? represents the first probable record of this genus outside the Mediterranean/Middle Eastern Tethyan province, and its early Barremian age partly fills the ‘gap’ in its previously known stratigraphical record, although the evolutionary relationship of the Japanese form with Mediterranean and Middle East Tethyan Pachytraga remains unsolved. However, the discovery of early Barremian Pachytraga? in Japan indicates that the evolutionary history of the genus is more complex than previously thought and should thus be discussed in a broader palaeogeographical context that must now include the Pacific.     

Insect biogeography in the south-western Sea of Korea with comments on the insect fauna of Kwanmae Island

The insect species richness of each island in the south‐western Sea of Korea was considered on the background of the equilibrium theory. The species number of insects on Kwanmae Island in the present study (140 species) was much higher compared with a previous survey. Based on a literature survey of island biota surveys published in the 1980s, of 47 islands, the lowest species number (12 species) was on Kwanmae Island, and the most diverse insect fauna (254 species) was on Baekryong Island. The mean species number of surveyed islands was approximately 54 (53.96 with a standard deviation of 46.95). The median species number was 38 with a skew of +2.56. Insects, including the orders Odonanta, Orthoptera, Hemiptera, Lepidoptera, Coleoptera, Hymenoptera and Diptera, occurred on 32 of the 47 surveyed islands, and had an occurrence rate of more than 0.68. This indicates that these insects are distributed widely on the islands in the south‐western Sea of Korea. The species number showed a significant linear relationship with both area of an island and its distance from the mainland (P < 0.05), with an extremely low determinant coefficient (r² = 0.13 for area vs species number and r² = 0.28 for distance vs species number). Other factors tested in the study failed to show a significant relationship with species number. A multiple‐regression model established using area and distance as independent variables showed significant relationship with species number, with a relatively higher determinant coefficient (r² = 0.70, P < 0.05). We present possible explanations to explain the difference between estimated and observed species number in Kwanmae Island.     

A laboratory study of the effects of shelter availability and invasive crayfish on the growth of native stream fish

1. The alteration of stream habitats by urbanisation reduces the availability of shelter. Reduced shelter availability may increase both predation risks and metabolic costs, negatively affecting the growth performance of stream fish. Although urbanised streams often allow the establishment of invasive species, the additive or interactive effects of shelter availability and invasive species are rarely explored. The invasive red swamp crayfish (Procambarus clarkii) is a strong shelter competitor and predator in streams. 2. We conducted a stream‐channel experiment to investigate how shelter availability and this invasive crayfish species affect the growth performance (measured as the loss in body mass under starved conditions) of two native benthic species, Japanese crucian carp (Carassius auratus complex) and an endangered cobitid fish (Lefua echigonia). 3. We found that both the absence of shelter and the presence of crayfish increased body mass loss in the crucian carp. However, the growth performance of the crucian carp was improved by the presence of shelter except in the presence of crayfish, in which case the shelter available did not ameliorate the negative effect of the crayfish on growth performance (i.e. an interactive effect). This result suggests that crayfish may affect the growth performance of the crucian carp through chemical cues as well as through shelter occupancy. 4. In contrast, shelter availability is the primary factor affecting the body mass loss of the cobitid fish. However, the growth performance of these fish was unaffected by the presence of crayfish. The change in the growth performance of the cobitid fish in response to the absence of shelter was greater than that of the crucian carp. This finding suggests that the cobitid fish may be more vulnerable than the crucian carp to a reduction in shelter availability. 5. Our study demonstrates that reduced shelter availability and/or crayfish invasion can have significant, indirect negative effects on the growth performance of native fish, but whether those effects are interactive might vary depending on the species. Our findings have clear implications for stream restoration and habitat assessment.     

Description of a New Planktonic Mixotrophic Dinoflagellate Paragymnodinium shiwhaense n. gen., n. sp. from the Coastal Waters off Western Korea: Morphology,Pigments, and Ribosomal DNA Gene Sequence

ABSTRACT. The mixotrophic dinoflagellate Paragymnodinium shiwhaense n. gen., n. sp. is described from living cells and from cells prepared by light, scanning electron, and transmission electron microscopy. In addition, sequences of the small subunit (SSU) and large subunit (LSU) rDNA and photosynthetic pigments are reported. The episome is conical, while the hyposome is hemispherical. Cells are covered with polygonal amphiesmal vesicles arranged in 16 rows and containing a very thin plate‐like component. There is neither an apical groove nor apical line of narrow plates. Instead, there is a sulcal extension‐like furrow. The cingulum is as wide as 0.2–0.3 × cell length and displaced by 0.2–0.3 × cell length. Cell length and width of live cells fed Amphidinium carterae were 8.4–19.3 and 6.1–16.0 μm, respectively. Paragymnodinium shiwhaense does not have a nuclear envelope chamber nor a nuclear fibrous connective (NFC). Cells contain chloroplasts, nematocysts, trichocysts, and peduncle, though eyespots, pyrenoids, and pusules are absent. The main accessory pigment is peridinin. The sequence of the SSU rDNA of this dinoflagellate (GenBank AM408889) is 4% different from that of Gymnodinium aureolum, Lepidodinium viride, and Gymnodinium catenatum, the three closest species, while the LSU rDNA was 17–18% different from that of G. catenatum, Lepidodinium chlorophorum, and Gymnodinium nolleri. The phylogenetic trees show that this dinoflagellate belongs within the Gymnodinium sensu stricto clade. However, in contrast to Gymnodinium spp., cells lack nuclear envelope chambers, NFC, and an apical groove. Unlike Polykrikos spp., which have a taeniocyst–nematocyst complex, P. shiwhaense has nematocysts without taeniocysts. In addition, P. shiwhaense does not have ocelloids in contrast to Warnowia spp. and Nematodinium spp. Therefore, based on morphological and molecular analyses, we suggest that this taxon is a new species, also within a new genus.     

Studies on sodium bypass flow in lateral rootless mutants lrt1 and lrt2, and crown rootless mutant crl1 of rice (Oryza sativa L.)

An apoplastic pathway, the so‐called bypass flow, is important for Na⁺ uptake in rice (Oryza sativa L.) under saline conditions; however, the precise site of entry is not yet known. We report the results of our test of the hypothesis that bypass flow of Na⁺ in rice occurs at the site where lateral roots emerge from the main roots. We investigated Na⁺ uptake and bypass flow in lateral rootless mutants (lrt1, lrt2), a crown rootless mutant (crl1), their wild types (Oochikara, Nipponbare and Taichung 65, respectively) and in seedlings of rice cv. IR36. The results showed that shoot Na⁺ concentration in lrt1, lrt2 and crl1 was lower (by 20–23%) than that of their wild types. In contrast, the bypass flow quantified using trisodium‐8‐hydroxy‐1,3,6‐pyrenetrisulphonic acid (PTS) was significantly increased in the mutants, from an average of 1.1% in the wild types to 3.2% in the mutants. Similarly, bypass flow in shoots of IR36 where the number of lateral and crown roots had been reduced through physical and hormonal manipulations was dramatically increased (from 5.6 to 12.5%) as compared to the controls. The results suggest that the path of bypass flow in rice is not at the sites of lateral root emergence.     

Complex phylogeographic patterns in the freshwater alga Synura provide new insights into ubiquity vs. endemism in microbial eukaryotes

The global distribution, abundance, and diversity of microscopic freshwater algae demonstrate an ability to overcome significant barriers such as dry land and oceans by exploiting a range of biotic and abiotic colonization vectors. If these vectors are considered unlimited and colonization occurs in proportion to population size, then globally ubiquitous distributions are predicted to arise. This model contrasts with observations that many freshwater microalgal taxa possess true biogeographies. Here, using a concatenated multigene data set, we study the phylogeography of the freshwater heterokont alga Synura petersenii sensu lato. Our results suggest that this Synura morphotaxon contains both cosmopolitan and regionally endemic cryptic species, co‐occurring in some cases, and masked by a common ultrastructural morphology. Phylogenies based on both proteins (seven protein‐coding plastid and mitochondrial genes) and DNA (nine genes including ITS and 18S rDNA) reveal pronounced biogeographic delineations within phylotypes of this cryptic species complex while retaining one clade that is globally distributed. Relaxed molecular clock calculations, constrained by fossil records, suggest that the genus Synura is considerably older than currently proposed. The availability of tectonically relevant geological time (10⁷–10⁸ years) has enabled the development of the observed, complex biogeographic patterns. Our comprehensive analysis of freshwater algal biogeography suggests that neither ubiquity nor endemism wholly explains global patterns of microbial eukaryote distribution and that processes of dispersal remain poorly understood.