Correlation between the loss of plasmid DNA and the transition from virulent phase I to avirulent phase II in Shigella sonnei

Transition from virulent phase I to non virulent phase II in five strains of Shigella sonnei was studied by immunofluorescence and plasmid electrophoresis. High frequency loss of phase I specific antigens was observed by use of fluorescent phase specific antibodies. Agarose gel electrophoresis of bacterial lysates showed that transition from phase I to phase II is associated with the loss of extrachromosomal DNA.     

The importance of the terminal hemi-acetal group for the ionophoric properties of nigericin

Summary Opening of the terminal hemi-acetal in dihydronigericin drastically reduces the ionophoric properties of nigericin and dehydroxymethylnigericin with 6 intact heterocycles. This is shown by 2 complementary methods, first with a liquid membrane electrode system, secondly by testing their ionophoric activities in rat liver mitochondria.Acknowledgments. The authors are indebted to Mrs G. Kergomard for her invaluable assistance in the isolement of nigericin and to Prof. A. Kergomard for his encouragements.     

On the normative dimension of the St. Petersburg paradox

In this paper I offer an account of the normative dimension implicit in D. Bernoulli’s expected utility functions by means of an analysis of the juridical metaphors upon which the concept of mathematical expectation was moulded. Following a suggestion by the late E. Coumet, I show how this concept incorporated a certain standard of justice which was put in question by the St. Petersburg paradox. I contend that Bernoulli would have solved it by introducing an alternative normative criterion rather than a positive model of decision making processes.     

Averaging over decision trees

Pruning a decision tree is considered by some researchers to be the most important part of tree building in noisy domains. While there are many approaches to pruning, the alternative of averaging over decision trees has not received as much attention. The basic idea of tree averaging is to produce a weighted sum of decisions. We consider the set of trees used for the averaging process, and how weights should be assigned to each tree in this set. We define the concept of afanned set for a tree, and examine how the Minimum Message Length paradigm of learning may be used to average over decision trees. We perform an empirical evaluation of two averaging approaches, and a Minimum Message Length approach.This work has been carried out with the support of the Defence Research Agency, Malvern.     

The demographic situation in the European Union

This article is an update of a similar article published in Population Trends 104 and complements the article on European-wide issues in population statistics, published in Population Trends 118. The main areas of demography are covered, namely population change, population composition, fertility and mortality. Eurostat are currently working on a new set of population projections which should be available shortly, but were not completed when this article was drafted.     

Is chlamydial heat shock protein 60 a risk factor for oncogenesis?

Heat shock protein 60 (HSP60) plays an important role in the protein folding of prokaryotic and eukaryotic cells. Most of the papers published on chlamydial HSP60 concern its role in immune response during infection. In the last decade, exposure to Chlamydia trachomatis has been consistently associated with the development of cervical and ovarian cancer. Moreover, it has been suggested that chlamydial HSP60 may have an anti-apoptotic effect during persistent infection. We hypothesize that the accumulation of exogenous chlamydial HSP60 in the cytoplasm of actively replicating eukaryotic cells may interfere with the regulation of the apoptotic pathway. The concomitant expression of viral oncoproteins and/or the presence of mutations may lead to the ability to survive apoptotic stimuli, loss of replicative senescence, uncontrolled proliferation and, finally neoplastic transformation.Received 15 August 2004; received after revision 1 October 2004; accepted 7 October 2004