A generic rate equation for catalysed,template-directed polymerisation

Biosynthetic networks link to growth and reproduction processes through template-directed synthesis of macromolecules such as polynucleotides and polypeptides. No rate equation exists that captures this link in a way that it can effectively be incorporated into a single computational model of the overall process. This paper describes the derivation of such a generic steady-state rate equation for catalysed, template-directed polymerisation reactions with varying monomer stoichiometry and varying chain length. The derivation is based on a classical Michaelis–Menten mechanism with template binding and an arbitrary number of chain elongation steps that produce a polymer composed of an arbitrary number of monomer types. The rate equation only requires the identity of the first dimer in the polymer sequence; for the remainder only the monomer composition needs be known. Further simplification of a term in the denominator yielded an equation requiring no positional information at all, only the monomer composition of the polymer; this equation still gave an excellent estimate of the reaction rate provided that either the monomer concentrations are at least half-saturating, or the polymer is very long.     

Patterns of circulating hepatitis B surface antigen variants among vaccinated children born to hepatitis B surface antigen carrier and non-carrier mothers

Hepatitis B virus (HBV) variants that possessed missense mutation within the neutralization epitope of the major S antigen as defined by amino acid residues (aa#) 124–147, termed the a determinant variants, were identified through a population-based serosurvey of 2,305 children of the vaccinated birth cohorts born after 1986. Data on the 678 nucleotides encoding the S antigen of HBV were available for 75 HBV strains that were collected from 63 vaccinated children and 12 unvaccinated or incompletely vaccinated children, and 21 HBV strains from 25 unvaccinated adults. Among the diverse patterns of one to three amino acid substitutions within the a determinant, 145-Arg occurred most frequently (5/14); other variants were: 126-Ala, 127-Thr, 126-Ser/131-Asn/133-Thr, 129-His, 129-Arg, 123-Asn/131-Ile, 133-Leu, 141-Glu, and 141-Arg/144-Ala. Only one of these variants occurred in the 16 hepatitis B surface antigen (HBsAg)-carrier children born to HBsAg-negative mothers, whereas 12 of these variants occurred in the 20 (50%) children born to HBsAg-positive mothers. In addition, early administration of HBV vaccine within the noenatal period increased the likelihood of the emergence of these variants to 64.7% (11/17). Five of the 21 (23.8%) unvaccinated HBsAg-carrier adults harbored the a determinant variants possessing mutations within aa# 125–136, i.e. the putative first loop formed by the cysteine disulfide bonds. Vaccinated children were likely to harbor HBV variants possessing mutations involving altered charge of side chains and/or its hydrophobicity of amino acid residues within the putative second loop between aa#140 and 146. Our data suggest that emergence of these HBV S gene mutants in the phase of HBV vaccination program would be most common among populations in whom perinatal/vertical transmission of HBV is most common, i.e. southeast Asian and the Taiwanese.     

p53 gene status modulates the chemosensitivity of non-small cell lung cancer cells

This study examined the effects of p53 gene status on DNA damage-induced cell death and chemosensitivity to various chemotherapeutic agents in non-small cell lung cancer (NSCLC) cells. A mutant p53 gene was introduced into cells carrying the wild-type p53 gene and also vice versa to introduce the wild-type p53 gene into cells carrying the mutant p53 gene. Chemosensitivity and DNA damage-induced apoptosis in these cells were then examined. This study included five cell lines, NCI-H1437, NCI-H727, NCI-H441 and NCI-H1299 which carry a mutant p53 gene and NCI-H460 which carries a wild-type p53 gene. Mutant p53-carrying cells were transfected with the wild-type p53 gene, while mutant p53 genes were introduced into NCI-H460 cells. These p53 genes were individually mutated at amino acid residues 143, 175, 248 and 273. The representative cell line NCI-H1437 cells transfected with wild-type p53 gene (H1437/wtp53) showed a dramatic increase in susceptibility to three anticancer agents (7-fold to cisplatin, 21-fold to etoposide, and 20-fold to camptothecin) compared to untransfected or neotransfected H1437 cells. An increase in chemosensitivity was also observed in wild-type p53 transfectants of H727, H441, H1299 cells. The results of chemosensitivity were consistent with the observations on apoptotic cell death. H1437/wtp53 cells, but not H1437 parental cells, exhibited a characteristic feature of apoptotic cell death that generated oligonucleosomal-sized DNA fragments. In contrast, loss of chemosensitivity and lack of p53-mediated DNA degradation in response to anticancer agents were observed in H460 cells transfected with mutant p53. These observations suggest that the increase in chemosensitivity was attributable to wild-type p53 mediation of the process of apoptosis. In addition, our results also suggest that p53 gene status modulates the extent of chemosensitivity and the induction of apoptosis by different anticancer agents in NSCLC cells.     

Postsealing genetic variation and population structure of two species of fur seal (Arctocephalus gazella and A. tropicalis)

Commercial sealing in the 18th and 19th centuries had a major impact on the Antarctic and subantarctic fur seal populations (Arctocephalus gazella and A. tropicalis) in the Southern Ocean. The intensive and unrestricted nature of the industry ensured substantial reductions in population sizes and resulted in both species becoming locally extinct at some sites. However, both species are continuing to recover, through the recolonization of islands across their former range and increasing population size. This study investigated the extent and pattern of genetic variation in each species to examine the hypothesis that higher levels of historic sealing in A. gazella have resulted in a greater loss of genetic variability and population structure compared with A. tropicalis. A 316-bp section of the mitochondrial control region was sequenced and revealed nucleotide diversities of 3.2% and 4.8% for A. gazella and A. tropicalis, respectively. There was no geographical distribution of lineages observed within either species, although the respective PhiST values of 0.074 and 0.19 were significantly greater than zero. These data indicate low levels of population structure in A. gazella and relatively high levels in A. tropicalis. Additional samples screened with restriction endonucleases were incorporated, and the distribution of restriction fragment length polymorphism (RFLP) and sequence haplotypes were examined to identify the main source populations of newly recolonized islands. For A. tropicalis, the data suggest that Macquarie Island and Iles Crozet were probably recolonized by females from Marion Island, and to a lesser extent Ile Amsterdam. Although there was less population structure within A. gazella, there were two geographical regions identified: a western region containing the populations of South Georgia and Bouvetoya, which were the probable sources for populations at Marion, the South Shetland and Heard Islands; and an eastern region containing the panmictic populations of Iles Kerguelen and Macquarie Island. The latter region may be a result of a pronounced founder effect, or represent a remnant population that survived sealing at Iles Kerguelen.     

Effects of pH and predation by Chaoborus larvae on the plankton of a shallow and acidic forest lake

1. Eutrophic acid lakes are not common. Delamere Lake in Cheshire, U.K. is shallow and acid (mean pH 4.5) with a very high phytoplankton crop (mean 290 μg chlorophyll a L^?1), dominated by Dictyosphaerium pulchellum. Rotifers were dominant in the pelagic waters but small cladocerans (Alona guttata, Chydorus sphaericus and Scapholeberis mucronata) were occasional in the littoral waters. Chaoborus flavicans larvae were the top predators in this fishless lake. Two mesocosm experiments were carried out in which pH and Chaoborus populations were manipulated. 2. Progressively higher concentrations of D. pulchellum were maintained in the elevated pH treatments (pH 6 and 8; P < 0.001) with increased amounts of a Chlamydomonas species at the end of the experiment. Highest species richness was seen at ambient pH. Thus the low pH of Delamere Lake alone did not control the structure of the phytoplankton community. Keratella quadrata showed significantly higher abundance at pH 6 than in other pH treatments (P < 0.001). Species richness of rotifers was unaffected by pH. 3. Most Cladocera were C. sphaericus. Although never seen in the open lake, Daphnia pulex appeared in all the pH treatments. Low pH did not control small Cladocera abundance in Delamere Lake, but probably hampered reproduction in Daphnia. Negative correlations between chlorophyll a concentrations and Daphnia in the mesocosms (r² = 0.215, P < 0.05), however, indicated the potential of large‐bodied daphniids in controlling phytoplankton. 4. Neither different combinations of Chaoborus instars (none, instars 1 and 2 and instars 3–5) nor different densities of instars 3–5 (0.15, 0.5 and 1.0 L^?1) had a negative impact on Cladocera. Daphnia pulex remained unaffected in the experiment, perhaps because of its large size, and C. sphaericus because of its high reproductive rate compensating predatory losses. 5. Very low pH in Delamere Lake might suppress Daphnia by hampering its reproduction. Consequently, Daphnia may be vulnerable to invertebrate predation even at low predator density in the lake.     

Fenced and Fragmented: Conservation Value of Managed Metapopulations

Population fragmentation is threatening biodiversity worldwide. Species that once roamed vast areas are increasingly being conserved in small, isolated areas. Modern management approaches must adapt to ensure the continued survival and conservation value of these populations. In South Africa, a managed metapopulation approach has been adopted for several large carnivore species, all protected in isolated, relatively small, reserves that are fenced. As far as possible these approaches are based on natural metapopulation structures. In this network, over the past 25 years, African lions (Panthera leo) were reintroduced into 44 fenced reserves with little attention given to maintaining genetic diversity. To examine the situation, we investigated the current genetic provenance and diversity of these lions. We found that overall genetic diversity was similar to that in a large national park, and included a mixture of four different southern African evolutionarily significant units (ESUs). This mixing of ESUs, while not ideal, provides a unique opportunity to study the impact of mixing ESUs over the long term. We propose a strategic managed metapopulation plan to ensure the maintenance of genetic diversity and improve the long-term conservation value of these lions. This managed metapopulation approach could be applied to other species under similar ecological constraints around the globe.