Juvenile proportion as a predictor of freshwater turtle population change

The extreme longevity of turtles and tortoises can make it difficult to determine the conservation status of their populations because high annual adult survival may mask gradual attrition due to low levels of recruitment. When long-term demographic trends are unknown and available data are insufficient for population modelling, it may be assumed that a scarcity of juveniles indicates low recruitment that will result in population ageing and numerical decline. However, the reliability with which the proportion of juveniles foreshadows demographic change is uncertain. We tested the hypothesis that a low proportion of juveniles in a turtle population presages its ageing by analysing over 20 years of survey data for five discrete populations of the Australian western saw-shelled turtle (Myuchelys bellii: Chelidae), a listed threatened species. The analysis tested whether the initial proportion of juvenile turtles in each population was related to its temporal trend in average body size. The five populations had varied structure and trends, with the initial proportion of juvenile turtles ranging from 10% to 39% and average body size increasing over time in some populations and decreasing in others. Contrary to expectation, the initial proportion of juveniles was unrelated to the trend in average body size and, by inference, average age, indicating that effective trend forecasting requires more detailed demographic information than merely population structure.     

Chemical shift assignments and secondary structure of the Grb2 SH2 domain by heteronuclear NMR spectroscopy

Summary The growth factor receptor-bound protein-2 (Grb2) is an adaptor protein that mediates signal transduction pathways. Chemical shift assignments were obtained for the SH2 domain of Grb2 by heteronuclear NMR spectroscopy, employing the uniformly ¹³C-/¹⁵N-enriched protein as well as the protein containing selectively ¹⁵N-enriched amino acids. Using the Chemical Shift Index (CSI) method, the chemical shift indices of four nuclei, ¹H, ¹³C, ¹³C and ¹³CO, were used to derive the secondary structure of the protein. Nuclear Overhauser enhancements (NOEs) were then employed to confirm the secondary structure. The CSI results were compared to the secondary structural elements predicted for the Grb2 SH2 domain from a sequence alignment [Lee et al. (1994) Structure, 2, 423–438]. The core structure of the SH2 domain contains an antiparallel -sheet and two -helices. In general, the secondary structural elements determined from the CSI method agree well with those predicted from the sequence alignment.Abbreviations crk viral p47^gag-crk - EGF epidermal growth factor - GAP GTPase-activating protein - PI3K phosphatidylinositol-3-kinase - PLC- phospholipase-C-, shc, src homologous and collagen - src sarcoma family of nonreceptor tyrosine kinase     

The NADP-linked glyceraldehyde-3-phosphate dehydrogenases of Anabaena variabilis and Synechocystis PCC 6803, which lack one of the cysteines found in the higher plant enzyme,are not reductively activated

Light activation of NADP-linked glyceraldehyde-3-P dehydrogenase involves reductive cleavage of a disulfide bond. We have proposed that the inactivating disulfide locks the two domains of the enzyme, preventing catalysis, and we have tentatively identified the two critical cysteine residues in the chloroplast enzyme (D. Li, F.J. Stevens, M. Schiffer and L.E. Anderson (1994) Biophys J. 67: 29–35). We reasoned that if activation of this enzyme involves these cysteines that enzymes lacking one or both should be active in the dark and insensitive to reductants. One of these cysteines is present in the enzymes from Anabaena variabilis and Synechocystis PCC 6803 but the other is not. Consistent with the proposed mechanism, glyceraldehyde-3-P dehydrogenase is not affected by DTT-treatment in extracts of either of these cyanobacteria. Fructosebisphosphatase is DTT-activated in extracts of both of these cyanobacteria and glucose-6-P dehydrogenase is inactivated in Synechocystis, as in higher plant chloroplasts. Apparently reductive modulation is possible in these cyanobacteria but glyceraldehyde-3-P dehydrogenase is not light activated.     

DIVERSITY AND PHYLOGENETIC PLACEMENT OF BRACTEACOCCUS TEREG (CHLOROPHYCEAE,CHLOROPHYTA) BASED ON 18S RIBOSOMAL RNA GENE SEQUENCE DATA1

Sequence data from the nuclear small-subunit ribosomal RNA gene was obtained for nine strains of Bracteacoccus Tereg, representing at least five morphological species and four distinct geographic locations. These, along with sequence data from two additional chlorophycean taxa, Spongiochloris spongiosa Starr and Ascochloris multinucleata Bold et MacEntee, and 48 published sequences from green algal taxa, were used to determine the phylogenetic placement of Bracteacoccus with respect to other chlorophycean green algae. Results support the monophyly of Bracteacoccus strains, contrasting with patterns observed so far for many other coccoid green algae. The range of variation among Bracteacoccus strains is similar to that of other congeners. Basal body orientation in Bracteacoccus has been interpreted as clockwise; however, the 18S data point to a relationship between Bracteacoccus and taxa with the directly opposed configuration of the flagellar apparatus. No close relationship was found to the multinucleated green coccoids with clockwise orientation of basal bodies, such as Spongiochloris, or to those with parallel basal bodies, such as Spermatozopsis. However, 18S data confirm that the motile and vegetative cells of Bracteacoccus are structurally distinct from the representatives of sphaeroplealean families currently studied. It is premature to reclassify Bracteacoccus until 18S comparisons can be made with additional sphaeroplealean taxa and with algae with similar flagellar structure such as Dictyochloris and Heterochlamydomonas.     

Formation of native hepatitis C virus glycoprotein complexes.

The hepatitis C virus (HCV) glycoproteins (E1 and E2) interact to form a heterodimeric complex, which has been proposed as a functional subunit of the HCV virion envelope. As examined in cell culture transient-expression assays, the formation of properly folded, noncovalently associated E1E2 complexes is a slow and inefficient process. Due to lack of appropriate immunological reagents, it has been difficult to distinguish between glycoprotein molecules that undergo productive folding and assembly from those which follow a nonproductive pathway leading to misfolding and aggregation. Here we report the isolation and characterization of a conformation-sensitive E2-reactive monoclonal antibody (H2). The H2 monoclonal antibody selectively recognizes slowly maturing E1E2 heterodimers which are noncovalently linked, protease resistant, and no longer associated with the endoplasmic reticulum chaperone calnexin. This complex probably represents the native prebudding form of the HCV glycoprotein heterodimer. Besides providing a novel reagent for basic studies on HCV virion assembly and entry, this monoclonal antibody should be useful for optimizing production and isolation of native HCV glycoprotein complexes for serodiagnostic and vaccine applications.