Studies in vitro of the nature and synthesis of the cell wall ofChlamydia trachomatis

The possibility thatChlamydia trachomatis contains peptidoglycan was examined by three methods. Preincubation of chlamydia with enzymes known to cleave peptidoglycan had no adverse effect on the subsequent development. Immunofluorescence studies with antistreptococcal peptidoglycan antisera failed to show any cross reactions with chlamydial antigens. The antichlamydial activity of anti-cell-wall antimicrobials was examined; lactams proved the most active, and cycloserine and bacitracin also showed antichlamydial activity. Alaphosphin, phosphomycin, and vancomycin showed no antichlamydial activity at the concentrations tested.     

Autoradiographic localization of ornithine decarboxylase in mouse kidney by use of radiolabeled α-difluoromethylornithine

Summary Ornithine decarboxylase, a key enzyme in polyamine biosynthesis and cell growth, has been localized in mouse kidney by autoradiography after administration of radiolabeled -difluoromethylornithine. This drug is an enzyme-activated irreversible inhibitor of ornithine decarboxylase and forms a covalent bond with the enzyme. It was found that ornithine decarboxylase is present in all cell types studied but that the highest content occurs in the proximal convoluted tubules followed by the distal convoluted tubules and the collecting tubules. The majority of the enzyme is located in the cytoplasm but about 10–15% is present in the nuclei (often associated with nucleolus-like components) of the cells of the proximal and distal convoluted tubules. The labeled ornithine decarboxylase was lost rapidly from both nucleus and cytoplasm of all the cell types examined, and labeling by radioactive -difluoromethylornithine was greatly reduced if the mice were pretreated for 5 h with cycloheximide to block protein synthesis. These results indicate that ornithine decarboxylase turns over rapidly in all of the cells.     

Occurrence and induction of spermidine-N1-acetyltransferase in Escherichia coli

Spermidine acetylase activity was detected in extracts prepared from $\text{Escherichia coli}$ and there was a marked increase in activity over the early period of growth. This increase reached a maximum 3 h after inoculation and was followed by an increase in ornithine decarboxylase activity. The acetylase was also able to use spermine as a substrate, but not putrescine. With spermidine and acetyl-CoA as substrate, the product formed was exclusively N¹-acetyl-spermidine. This is the first evidence for the occurrence in bacteria of spermidine-N¹-acetyltransferase, an enzyme which has previously been described in mammalian cells. These results suggest that acetylation of spermidine may be involved in the growth of $\text{Escherichia coli}$ and in the regulation of its polyamine content.     

Transformation and allelic replacement in Francisella spp.

We describe methods for transposon mutagenesis and allelic replacement in the facultative intracellular pathogen Francisella. Recombinant clones were constructed by insertion of partially cut F. tularensis or F. novicida DNA into pUC19 and then mutagenized with a mini-Tn10-Km transposon. F. novicida could be transformed with these plasmids either by a chemical transformation method or by electroporation, whereas F. tularensis could be transformed only by electroporation. Transformation of F. tularensis by electroporation was enhanced in the absence of the capsule. Southern blot analysis showed that the KmR marker was rescued either by integration of the plasmid into the Francisella chromosome or by allelic replacement. Allelic replacement was found to be the mechanism underlying a site-specific mutation affecting FopA, an outer-membrane protein of Francisella. F. novicida could also be transformed with chromosomal DNA carrying the KmR marker and the transformation frequency obtained using chromosomal DNA was generally greater than that obtained using plasmid DNA. F. novicida was also transformed by an IncQ plasmid containing an F. novicida DNA insert, which replicated autonomously in this host.     

Computer modelling of neural tube defects

Neurulation, the curling of the neuroepithelium to form the neural tube, is an essential component of the development of animal embryos. Defects of neural tube formation, which occur with an overall frequency of one in 500 human births, are the cause of severe and distressing congenital abnormalities. However, despite the fact that there is increasing information from animal experiments about the mechanisms which effect neural tube formation, much less is known about the fundamental causes of neural tube defects (NTD). The use of computer models provides one way of gaining clues about the ways in which neurulation may be compromised. Here we employ one computer model to examine the robustness of different cellular mechanisms which are thought to contribute to neurulation. The model, modified from that of Odell et al (Odell, G.M., Oster, G., Alberch, P. and Burnside, B., (1981)) mimics neurulation by laterally propagating a wave of apical contraction along an active zone within a ring of cells. We link the results to experimental evidence gained from studies of embryos in which neurulation has been perturbed. The results indicate that alteration of one of the properties of non-neural tissue can delay or inhibit neurulation, supporting the idea, gained from observation of embryos bearing genes which predispose to NTD, that the tissue underlying the neuroepithelium may contribute to the elevation of the neural folds. The results also show that reduction of the contractile properties of a small proportion of the neuroepithelial cell population may have a profound effect on overall tissue profiling. The results suggest that the elevation of the neural folds, and hence successful neurulation, may be vulnerable to relatively minor deficiencies in cell properties.     

Migration in Archeology: The Baby and the Bathwater

Migration has been largely ignored by archeologists for the last two decades. Yet prehistoric demography and population studies are accepted as central concerns, and neither of these can be studied profitably without an understanding of migration. Recent books by Rouse and Renfrew have resurrected migration as a subject of serious analysis. It is proposed here that systems-oriented archeologists, in rejecting migration, have thrown out the baby with the bathwater. Traditional archeological approaches to migration fall short because a methodology for examining prehistoric migration must be dependent upon an understanding of the general structure of migration as a patterned human behavior. Aspects of such a structure are suggested and an application to a particular case in Eastern Europe is described.