Identification and phylogeny of eukaryotic 18S rDNA phylotypes detected in chlorinated finished drinking water samples from three Parisian surface water treatment plants

Aims:  We performed a preliminary assessment of the eukaryotic 18S rDNA diversity present in finished drinking water samples from three different surface water treatment plants supplying water to the city of Paris (France).
Methods and Results:  A molecular analysis was performed on a sample from each site based on sequencing of PCR amplified and cloned 18S ribosomal RNA genes. Overall, the 18S rDNA sequences combined from all samples could be affiliated to the Amoebozoa (20·8% of the phylotypes), Ciliophora (25%), Metazoa (33·3%), Fungi (8·3%), Cercozoa (4·2%) and unclassified eukaryotes (8·3%) groups.
Conclusions:  The 18S rDNA sequences affiliated to the Amoebozoa, Ciliophora and Metazoa lineages were found to be the most abundant phylotypes observed in the drinking water samples. Phylotypes found to be present in two, or all three, samples (41·7% of the total) may represent groups with members adapted to drinking water treatment plant (DWTP) ecosystem conditions.
Significance and Impact of the Study:  This study shows that finished drinking water can contain 18S rDNA sequences representing a variety of eukaryotic taxa. Further research is needed to better characterize the eukaryotic biodiversity of DWTPs and the effects of the finished drinking water diversity on the downstream water distribution network.     

Identification of a single-stranded DNA binding protein from rat liver with high mobility group protein 1

The rat liver single-stranded DNA binding protein, S25 and HD25, isolated by differential DNA cellulose affinity chromatography was compared to the high mobility group proteins, HMG1 and HMG2, isolated from rat liver chromatin by the technique of Goodwin et al. (Goodwin, G. H., Sanders, C., and Johns, E. W. (1973) Eur. J. Biochem. 38, 14-19). Analysis of their amino acid composition, electrophoretic mobility, and tryptic peptide map reveal the identity of the single-stranded DNA binding protein with HMG1 protein, implying that the rat liver HMG1 protein becomes able both to destabilize a double helix of DNA and to stimulate homologous DNA polymerases only when rat liver cells enter a phase of DNA synthesis, possibly after a specific modification.     

Molecular biology of liver regeneration

Liver regeneration is a good system for studying cell proliferation in an in vivo, physiologically controlled situation. Various hepatotrophic factors, neuromediators, hormones and growth factors, presumably acting in synergy, seem necessary to induce the switch from quiescence to proliferation. As a consequence of this activation, a number of changes occurs in the hepatocyte: modifications of the plasma membrane proteins; metabolic changes such as variations in albumin and fibrinogen concentrations, and induction of the acute phase proteins; induction of several specific mRNAs; variations in cAMP concentrations, and consequently in the activity of protein kinases and several other enzymes; modifications in chromosomal proteins; induction of proteins involved in DNA replication. A model has been constructed which is more a basis for reflexion than a theoretical model. It takes into account the possible connections between the different molecular events cited above. It is hypothesized that DNA replication is at least partly uncoupled from mitosis, and that the initial events of the proliferative response may be triggered by nutritional elements.     

Effect of histone H1, poly(ethyleneglycol) and DNA concentration on intermolecular and intramolecular ligation by T4 DNA ligase

The efficiency of ligation of linear DNA and the relative amounts of intramolecular versus intermolecular ligation may be triggered by a number of additive agents. The results show that it is possible to mimic the effect of poly(ethyleneglycol) 6000 by simply increasing DNA concentration about 15-fold: both the rate and the extent of the reaction are greatly enhanced, and intermolecular ligation is largely favored. However, in this case the stimulation by salts, which occurs in poly(ethyleneglycol) solutions, is not observed; we suggest that salts enhance the hydrophobic interactions between ligase and DNA that take place in the presence of poly(ethyleneglycol). We also show that histone H1, which is involved in the formation of chromatin fibers, is able to stimulate intermolecular ligation by T4 ligase. This effect is more specific than a simple neutralisation of the phosphate groups of the DNA by positive charges of the histone; it still occurs at 125 mM NaCl and in the presence of the four core histones. The implications of the finding concerning the mode of action of histone H1 on DNA are discussed.     

Comparison of biochemical properties of DNA-topoisomerase I from normal and regenerating liver.

Biochemical properties of topoisomerase I from normal and regenerating rat liver were analysed using crude or fractionated nuclear extracts. We could not detect significative change in topoisomerase I content or activity (magnesium stimulation and inhibition by ATP) during the course of liver regeneration. Topoisomerase I can be resolved into two species of 97 kDa and 100 kDa, with the same pI of 8.2-8.6 as shown by two dimensional gel electrophoresis. The two polypeptides contained a non-phosphorylated precursor and others forms with variable degrees of phosphorylation. In-vitro dephosphorylation with alkaline phosphatase leads to the disappearance of the phosphorylated forms and inactivation of the enzyme. The affinity of topoisomerase I for chromatin (measured by salt elution) differs markedly between normal and regenerating liver: nearly 50% of topoisomerase I remained bound to the chromatin from normal liver at 250 mM NaCl whereas it was completely eluted from 24-h-regenerating-liver nuclei. The biological significance of these results is discussed.