UV-Irradiated SV40 minichromosomes as substrates for DNA repair endonucleases

UV-irradiated SV40 minichromosomes have been shown to be a substrate for a purified DNA repair endonuclease. A UV-repair endonuclease activity was also found to be associated with the isolated SV40 minichromosomes themselves. It appeared to have similar properties to the enzymes described from other mammalian sources.     

The Cryptomonas–Caulobacter consortium: facultative ectocommensalism with possible taxonomic consequences?

Cryptomonas cells with an anomalous shape, usually possessing a transversal constriction, have been observed in nature and in cultures. Closer examination of the cells revealed the presence of a dense carpet of bacteria of the genus Caulobacter within the transversal groove. This observation raises the question of a possible mutual benefit from the association, as well as the question of the taxonomic validity of previously described species of Cryptomonas with similar cell shape. When brought into bacteriafree culture, a Cryptomonas strain lost the transversal constriction and assumed the characteristic shape of C. curvata. No benefit to the growth of Cryptomonas could be recorded in the presence of the bacteria.     

Properties of enzymes that recognize modified structures in DNA

The properties of the major classes of DNA repair enzymes, such as DNA glycosylases, AP-endonucleases, incision nucleases, and alkyl transferases, are reviewed. With the exceptions of the incision nucleases, the properties of the enzymes are quite similar in prokaryotic and eukaryotic cells. The incision nucleases probably do not recognize the modified base residues as such, but rather helical distortion brought about by the modifying agents. The other classes of enzymes are more or less specific for certain modified structures.     

Methanol poisoning and long term sequelae – a six years follow-up after a large methanol outbreak

Background  

Mass poisonings with methanol are rare but occur regularly both in developed and in developing countries. Data from the poisoning episodes are often published, but follow-up-data is scarce. We therefore conducted a six year follow-up study after the large methanol outbreak in Estonia in September 2001.     

Temperature‐size relations from the cellular‐genomic perspective

A family of empirically based ecological ‘rules’, collectively known as temperature‐size rules, predicts larger body size in colder environments. This prediction is based on studies demonstrating that a wide range of ectotherms show increased body size, cell size or genome size in low‐temperature habitats, or that individuals raised at low temperature become larger than conspecifics raised at higher temperature. There is thus a potential for reduction in size with global warming, affecting all levels from cell volume to body size, community composition and food webs. Increased body size may be obtained either by increasing the size or number of cells. Processes leading to changed cell size are of great interest from an ecological, physiological and evolutionary perspective. Cell size scales with fundamental properties such as genome size, growth rate, protein synthesis rates and metabolic activity, although the causal directions of these correlations are not clear. Changes in genome size will thus, in many cases, not only affect cell or body size, but also life‐cycle strategies. Symmetrically, evolutionary drivers of life‐history strategies may impact growth rate and thus cell size, genome size and metabolic rates. Although this goes to the core of many ecological processes, it is hard to move from correlations to causations. To the extent that temperature‐driven changes in genome size result in significant differences among populations in body size, allometry or life‐cycle events such as mating season, it could serve as a fast route to speciation. We offer here a novel perspective on the temperature‐size rules from a ‘bottom‐up’ perspective: how temperature may induce changes in genome size, and thus implicitly in cell size and body size of metazoans. Alternatively: how temperature‐driven enlargement of cells also dictates genome‐size expansion to maintain the genome‐size to cell‐volume ratio. We then discuss the different evolutionary drivers in aquatic versus terrestrial systems, and whether it is possible to arrive at a unifying theory that also may serve as a predictive tool related to temperature changes. This, we believe, will offer an updated review of a basic concept in ecology, and novel perspectives on the basic biological responses to temperature changes from a genomic perspective.     

Contributions to the Caloplaca flora of the western Antarctic region

Fourteen species of the lichen genus Caloplaca are recorded from the western Antarctic region and described morphologically and anatomically, viz.: C. ammiospila, C. approximata, C. athallina, C. cirrochrooides, C. citrina, C. isidioclada, C. lucens, C. millegrana, C. regalis, C. sublobulata, C. tenuis, C. aff. anchon-phoeniceon. Type specimens of critical species have been studied. A key is provided to the species. Caloplaca ammiospila and C. approximata are reported as new to the Antarctic region.     

Causes for mass occurrences of the jellyfish Periphylla periphylla: a hypothesis that involves optically conditioned retention

The mesopelagic coronate medusa Periphylla periphylla has beenvery abundant (20–320 individuals m^–2), with asmany as 2.5 individuals m^–3, for more than a decade incertain Norwegian fjords. These abundances are two to threeorders of magnitude higher than reported from open ocean environments.Comparisons of the size, density and behavior of this jellyfishin three fjords (Lurefjorden, Sognefjorden and Halsafjorden)support the hypothesis that retention of P. periphylla is relatedto basin topography, light attenuation and photosensitivity.Furthermore, we hypothesize that the abundances of P. periphyllain Lurefjorden and Halsafjorden, but not in Sognefjorden, havebeen stimulated by increased light absorbance of water massesformed in the North Sea.     

Competition or niche segregation between Holopedium and Daphnia; empirical light on abiotic key parameters

A survey of 346 Norwegian lakes revealed some consistent patterns with regard to the occurrence of Holopedium gibberum versus Daphnia spp. Both biomass and frequency of Holopedium were negatively correlated with pH and Ca-concentration, and this species rarely occurred at pH > 8, or Ca-concentrations > 10 mg l^–1. On the contrary, the various Daphnia species, although showing different susceptibilities to fish predation and different preferences for lake productivity, were all positively correlated with Ca. Statistical analysis as well as laboratory experiments and biochemical considerations, suggest that Holopedium may be a superior competitor at very low Ca-concentrations, but is replaced by Daphnia at higher pH and increasing Ca-content. High pH in itself is possibly disadvantageous for Holopedium by preventing formation of the muco-polysaccaride mantle.     

Elimination of MNU-induced mutational lesions in V79 Chinese hamster cells

Studies were performed on the non-linear dose response for gene mutations induced by low doses of monofunctional methylating agents in V79 Chinese hamster cells. When treatment with methylnitrosourea was applied at the beginning of the S phase in synchronized cells, a linear dose-response curve was obtained, whereas application of the dose after gene replication resulted in a strong reduction of the number of induced mutations. Additional time for repair resulted in reduced dose response of MNU, indicating that an error-free repair process operates on methylated DNA in V79 Chinese hamster cells.