The short 5′ untranslated region of the βA3/A1-crystallin mRNA is responsible for leaky ribosomal scanning

Leaky ribosomal scanning allows the expression of multiple proteins from a single mRNA by occasionally skipping the first start codon, and initiating translation at a subsequent one. A3- and A1-crystallin, two members of the -crystallin family of vertebrate eye lens proteins, are produced via this mechanism, of which, until now, only very few examples have been found in eukaryotic genes. Since the two start codons on the A3/A1 messenger lie in the same reading frame, the two translated proteins are identical, except for the 17 residues shorter N-terminal extension of A1-crystallin. It has been suggested that the very short leader (5–7 nucleotides) of the A3/A1 messenger might cause slippage at the first start codon, although the unfavorable context of this start codon might also be responsible. Using transient transfections, we now demonstrate that increasing the length of the leader sequence to 67 nucleotides indeed completely abolishes translation initiation at the second start codon, and thus expression of the A1-crystallin protein. Messengers having a leader of 5, 7 or 14 nucleotides all express both A3- and A1-crystallin at very similar relative levels.     

Influence of White Clover Mosaic Potexvirus Infection on the Endogenous Cytokinin Content of Bean

The cytokinin content in the primary leaves of bean (Phaseolus vulgaris) was monitored for 10 d after inoculation with white clover mosaic potexvirus. The cytokinins were isolated, purified, separated by high-performance liquid chromatography, and quantified by radioimmunoassay. The cytokinins detected at the time of inoculation (d 0) were: (a) the free bases, zeatin (Z), dihydrozeatin (DZ), and isopentenyladenine; (b) the riboside, DZ riboside (DZR); (c) the O-glucosides of DZ, DZR, and Z riboside; (d) the nucleotides, Z riboside-5′-monophosphate and isopentenyladenosine-5′-monophosphate; and (e) trace amounts of Z-9-glucoside and DZ-9-glucoside. During the 10 d after inoculation with white clover mosaic potexvirus, marked quantitative changes in this cytokinin profile were observed. The concentration of the free bases and DZR decreased, accompanied by an increase in the 9-glucosides and the nucleotides. Virus titer increased rapidly 3 d after inoculation, attaining a maximum level at d 5. This increase coincided with the increases in the 9-glucosides and the nucleotides. We propose that the decline in the cytokinin free bases and riboside may allow the increase of virus titer in bean and lead to the senescence of infected leaves.     

Basis for the Checkpoint Signal Specificity That Regulates Chk1 and Cds1 Protein Kinases

Six checkpoint Rad proteins (Rad1, Rad3, Rad9, Rad17, Rad26, and Hus1) are needed to regulate checkpoint protein kinases Chk1 and Cds1 in fission yeast. Chk1 is required to prevent mitosis when DNA is damaged by ionizing radiation (IR), whereas either kinase is sufficient to prevent mitosis when DNA replication is inhibited by hydroxyurea (HU). Checkpoint Rad proteins are required for IR-induced phosphorylation of Chk1 and HU-induced activation of Cds1. IR activates Cds1 only during the DNA synthesis (S) phase, whereas HU induces Chk1 phosphorylation only in cds1 mutants. Here, we investigate the basis of the checkpoint signal specificity of Chk1 phosphorylation and Cds1 activation. We show that IR fails to induce Chk1 phosphorylation in HU-arrested cells. Release from the HU arrest following IR causes substantial Chk1 phosphorylation. These and other data indicate that Cds1 prevents Chk1 phosphorylation in HU-arrested cells, which suggests that Cds1 actively suppresses a repair process that leads to Chk1 phosphorylation. Cds1 becomes more highly concentrated in the nucleus only during the S phase of the cell cycle. This finding correlates with S-phase specificity of IR-induced activation of Cds1. However, constitutive nuclear localization of Cds1 does not enhance IR-induced activation of Cds1. This result suggests that Cds1 activation requires DNA structures or protein activities that are present only during S phase. These findings help to explain how Chk1 and Cds1 respond to different checkpoint signals.     

Memory Consolidation in the Cerebellar Cortex

Several forms of learning, including classical conditioning of the eyeblink, depend upon the cerebellum. In examining mechanisms of eyeblink conditioning in rabbits, reversible inactivations of the control circuitry have begun to dissociate aspects of cerebellar cortical and nuclear function in memory consolidation. It was previously shown that post-training cerebellar cortical, but not nuclear, inactivations with the GABA_A agonist muscimol prevented consolidation but these findings left open the question as to how final memory storage was partitioned across cortical and nuclear levels. Memory consolidation might be essentially cortical and directly disturbed by actions of the muscimol, or it might be nuclear, and sensitive to the raised excitability of the nuclear neurons following the loss of cortical inhibition. To resolve this question, we simultaneously inactivated cerebellar cortical lobule HVI and the anterior interpositus nucleus of rabbits during the post-training period, so protecting the nuclei from disinhibitory effects of cortical inactivation. Consolidation was impaired by these simultaneous inactivations. Because direct application of muscimol to the nuclei alone has no impact upon consolidation, we can conclude that post-training, consolidation processes and memory storage for eyeblink conditioning have critical cerebellar cortical components. The findings are consistent with a recent model that suggests the distribution of learning-related plasticity across cortical and nuclear levels is task-dependent. There can be transfer to nuclear or brainstem levels for control of high-frequency responses but learning with lower frequency response components, such as in eyeblink conditioning, remains mainly dependent upon cortical memory storage.     

Links between global taxonomic diversity,ecological diversity and the expansion of vertebrates on land

Tetrapod biodiversity today is great; over the past 400 Myr since vertebrates moved onto land, global tetrapod diversity has risen exponentially, punctuated by losses during major extinctions. There are links between the total global diversity of tetrapods and the diversity of their ecological roles, yet no one fully understands the interplay of these two aspects of biodiversity and a numerical analysis of this relationship has not so far been undertaken. Here we show that the global taxonomic and ecological diversity of tetrapods are closely linked. Throughout geological time, patterns of global diversity of tetrapod families show 97 per cent correlation with ecological modes. Global taxonomic and ecological diversity of this group correlates closely with the dominant classes of tetrapods (amphibians in the Palaeozoic, reptiles in the Mesozoic, birds and mammals in the Cenozoic). These groups have driven ecological diversity by expansion and contraction of occupied ecospace, rather than by direct competition within existing ecospace and each group has used ecospace at a greater rate than their predecessors.     

Killing of spores of Bacillus subtilis by tert-butyl hydroperoxide plus a TAML activator

AIMS: To determine the effectiveness of tert-butyl hydroperoxide (tBHP) plus the cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and a tetra-amido macrocyclic ligand (TAML) activator in killing spores of Bacillus subtilis and the mechanisms of spore resistance to and killing by this reagent. METHODS AND RESULTS: Killing of spores of B. subtilis by tBHP was greatly stimulated by the optimum ratio of concentrations of a TAML activator (1.7 micromol l(-1)) to tBHP (4.4%, vol/vol) plus a low level (270 mg l(-1)) of CTAB. Rates of killing of spores lacking most DNA protective alpha/beta-type small, acid-soluble spore proteins (alpha(-)beta(-) spores) or the major DNA repair protein, RecA, by tBHP plus CTAB and a TAML activator were essentially identical to that of wild-type spore killing. Survivors of wild-type and alpha(-)beta(-) spores treated with tBHP plus CTAB and a TAML activator also exhibited no increase in mutations. Spores lacking much coat protein either because of mutation or chemical decoating were much more sensitive to this reagent than were wild-type spores, but were more resistant than growing cells. Wild-type spores killed with this reagent retained their large pool of dipicolinic acid (DPA), and the survivors of spores treated with this reagent were sensitized to wet heat. The tBHP plus CTAB and TAML activator-killed spores germinated with nutrients, albeit more slowly than untreated spores, but germinated faster than untreated spores with dodecylamine. The killed spores were also germinated by application of 150 and 500 megaPascals of pressure for 15 min and by lysozyme treatment in hypertonic medium, but these spores lysed shortly after their germination. CONCLUSIONS: The combination of tBHP plus CTAB and a TAML activator is effective in killing B. subtilis spores. The spore coat is a major factor in spore resistance to this reagent system, which does not kill spores by DNA damage or by inactivating some component needed for spore germination. Rather, this reagent system appears to kill spores by damaging the spore's inner membrane in some fashion. SIGNIFICANCE AND IMPACT OF THE STUDY: This work demonstrates that tBHP plus CTAB and a TAML activator is an effective and mild decontaminant for spores of Bacillus species. Evidence has also been obtained on the mechanisms of spore resistance to and killing by this reagent system.     

Neuronal identification of acoustic signal periodicity

Acoustic signals transmit information by temporal characteristics and envelope periodicity as well as by their frequency content. Many animals can extract the frequency content of a signal by means of specialized organs such as the cochlea but for the detection and identification of higher-order periodicity, e.g., amplitude modulations, this type of organ is useless. In addition, many animals do not have a cochlea but still depend on a reliable identification of different frequencies in the vast variety of acoustic signals they perceive in their natural environment. Hence, neural mechanisms to decode periodicity information must exist. We present a detailed mathematical analysis of a recurrent and a feedforward model of neuronal periodicity extraction and discuss basic constraints for neuronal circuitry performing such a task in a biological system. Both the recurrent and the feedforward model perform well using neuronal parameters typical for the auditory system. Performance is limited mainly by the temporal precision of the connections between the neurons.     

Peptidomic analysis of skin secretions from Rana heckscheri and Rana okaloosae provides insight into phylogenetic relationships among frogs of the Aquarana species group

The members of the Aquarana (or Rana catesbeiana species group) form a monophyletic group comprising seven species: R. catesbeiana, Rana clamitans, Rana grylio, Rana virgatipes, Rana septentrionalis, Rana heckscheri and Rana okaloosae. Previous work has led to structural characterization of the antimicrobial peptides present in electrically-stimulated skin secretions from the first five species listed and this study presents the primary structures of orthologs from the river frog R. heckscheri and the Florida bog frog R. okaloosae. Peptidomic analysis of R. heckscheri and R. okaloosae skin secretions led to the identification of peptides with antimicrobial activity belonging to the ranalexin, ranatuerin-2, and temporin families. In addition, a peptide (GFLDIIKDTGKDFAVKILNNLKCKLAGGCPR) was isolated from R. okaloosae whose primary structure identified it as a member of the palustrin-2 family. Consistent with previous data based upon morphological analysis and comparisons of the nucleotide sequences of mitochondrial and ribosomal genes, cladistic analysis based upon a comparison of the amino acid sequences of antimicrobial peptides indicates a sister-group relationship between R. heckscheri and R. grylio and a close, but less well defined, phylogenetic relationship between R. okaloosae and R. clamitans.     

Depth-related changes to density,diversity and structure of benthic megafaunal assemblages in the Fimbul ice shelf region,Weddell Sea,Antarctica

The depth-related patterns in the benthic megafauna of the NE Weddell Sea shelf at the edge of the Fimbul Ice Shelf were investigated at seven sites using towed camera platform photographs. Megafaunal density decreased with depth from 77,939 ha⁻¹ at 245 m to 8,895 ha⁻¹ at 510 m. While diversity was variable, with H′ ranging between 1.34 and 2.28, there were no depth related patterns. Multivariate analyses revealed two distinct assemblages; a shallow assemblage with dense patches of suspension feeders in undisturbed areas and a deep assemblage where these were not present. Disturbance from icebergs explained many observed patterns in faunal distribution. In shallow waters probable effects of disturbance were observed as changes in successional stages; in deeper waters changes in habitat as a result of past disturbance explained faunal distributions. In deeper areas ice ploughing created a mosaic landscape of fine and coarse sediments. Total megafaunal density was highest in areas of coarse sediment (up to 2.9 higher than in finer sediment areas) but diversity was highest in intermediate areas (H′ = 2.35).