Regulation of the genes for E. coli DNA gyrase: Homeostatic control of DNA supercoiling

DNA gyrase is the bacterial enzyme responsible for converting circular DNA to a negatively supercoiled form. We show that the synthesis of DNA gyrase is itself controlled by DNA supercoiling; synthesis is highest when the DNA template is relaxed. The rates of synthesis in vivo of both the A and B subunits of DNA gyase are increased up to 10-fold by treatments that block DNA gyrase activity and decrease the supercoiling of intracellular DNA. Similarly, efficient synthesis of both gyrase subunits in a cell-free S-30 extract depends on keeping the closed circular DNA template in a relaxed conformation. The results suggest that DNA supercoiling in E. coli is controlled by a homeostatic mechanism. Synthesis of the RecA protein and several other proteins is also increased by treatments that relax intracellular DNA.     

Evolution of epitopes on human and nonhuman primate lymphocyte cell surface antigens

The T- and B-cell surface polypeptides detected by an international workshop panel of 100 mouse monoclonal antibodies (M.Ab) were biochemically defined by radioimmunoprecipitation. Eight T-cell-associated molecules and eight B-cell-associated molecules were identified by multiple antibodies in the panel. Clusters of antibodies specific for the same polypeptide were then compared for their reactivity against peripheral blood mononuclear cells (PBMC) from 11 nonhuman primate species. All the major T- and B-cell antigens present in humans were also expressed in some nonhuman primates. M.Ab to the same antigen were found to react with distinct epitope groups that differed in their phylogenetic distribution. Some epitopes were highly conserved, while other epitopes on the same molecule were only expressed in hominoids and were not detected in old world and new world monkeys. Our detailed analysis of the phylogeny of 37 T-cell antigen epitopes on ten different molecules revealed there was no clear correspondence between the number of epitopes shared and evolutionary distance. Rather the data suggest that parallelism with back mutation may be a common mechanism in the evolution of T-cell antigens. The data also show that the tissue distribution of T-cell antigens can differ between primate species; for example, M.Ab to human Tp45 Tla-Qa-like antigens that did not react with human PBMC did react with PBMC from new world monkeys.     

Formation of a supramolecular complex is involved in the reconstitution of basement membrane components

Basement membrane macromolecules, including type IV collagen, laminin, and heparan sulfate proteoglycan, do not aggregate when incubated alone. Rather, precipitation occurs in the presence of equimolar amounts of laminin and type IV collagen but variable amounts of heparan sulfate proteoglycan. This interaction requires native laminin and type IV collagen. Heparan sulfate proteoglycan increases the precipitation of laminin particularly in the presence of type IV collagen. Fibronectin does not cause type IV collagen to precipitate. These studies show that the components of basement membrane interact in a highly specific manner and suggest that such interactions may be involved in the deposition of basement membrane in situ.     

Polysome structure in sea urchin eggs and embryos: an electron microscopic analysis

Primary cultures of cardiac myocytes from newborn normal and genetically cardiomyopathic (strain UM-X7.1) hamsters were analyzed by electron microscopy and immunofluorescent staining for myosin, actin, tropomyosin, and alpha-actinin. Antibody staining of these contractile proteins demonstrates that both normal and cardiomyopathic (CM) myocytes contain prominent myofibrils after 3 days in culture, although the CM myofibrils are disarrayed and not aligned as those in normal cells. The disarray becomes even more pronounced in CM cells after 5 days in culture. The immunofluorescent staining patterns of individual myofibrils in normal and CM cells were similar for myosin, actin, and tropomyosin. However, alpha-actinin staining reveals that the CM myofibrils have abnormally wide and irregularly shaped Z bands. Electron microscopy confirms the irregular Z-band appearance as well as the myofibril disarray. Thus, CM cardiomyocytes clearly show an aberrant pattern of myofibril structure and organization in culture.     

The role of GTP in prostaglandin E1 stimulation of adenylate cyclase in platelet membranes.

Adenylate cyclase activity in platelet membrane preparations was measured in the presence of prostaglandin E1 (PGE1), GTP and a non-hydrolysable analogue of GDP, guanosine 5'-[beta-thio]diphosphate (GDP[beta S]). A dose-dependent inhibition of adenylate cyclase by GDP[beta S] was observed that could be reversed either by adding increased amounts of GTP or of PGE1.     

Sayl andghayl: The ecology of water allocation in Yemen

In this article, comparison is made between the two major types of water allocation systems in Yemen: seasonal flood (sayl)and highland spring flow (ghayl).Constraints in the nature of water as a flowing resource are defined for each system. The major distinctions between the two types of systems are variability in water flow (which influences the determination of access rights), techniques of water control, measurement of water turns, the need for supervision of irrigation activities, and the potential for economic expansion of the production system. It is argued that tribal political organization is an adaptive response to highland spring flow allocation in Yemen, but undergoes stress in coastal flood systems where competition for the same water source extends across tribal boundaries in upstream-downstream conflict.     

Proliferation of cells undergoing chondrogenesis in vitro

Abstract. Continuous exposure of chicken embryo limb bud mesenchyme cells undergoing chondrogenesis in vitro to [³H] thymidine ([³H]TdR) revealed that more than 90% of the cells synthesized DNA at least once during 120 h of culture. When cells were exposed to [³H]TdR for 24 h beginning at various times throughout the culture period, the percentage of cells which incorporated [³H]TdR during each period was approximately 92%. However, when the period for incorporation of radioisotope was limited to two hours, the number of cells which incorporated [³H]TdR was found to decline during chondrogenesis in vitro. This decline was coincident with the appearance of extracellular matrix material and occurred in those cells which had, and had not, expressed the cartilage phenotype.
We conclude from these studies that (1) practically all of the cells continue to proliferate while chondrogenesis is occurring in vitro, (2) there is an increase in the length of the cell cycle during chondrogenesis in vitro, and (3) withdrawal from the cell cycle is not required for differentiation of mesenchyme into cartilage.     

Transmission of Salmonella montevideo in Wheat by Stored-Product Insects

Sitophilus oryzae (L.), S. granarius (L.), Tribolium castaneum (Hbst.), Oryzaephilus surinamensis (L.), Rhyzopertha dominica (F.), Tenebroides mauritanicus (L.), and Cryptolestes pusillus (Schon.) transmitted Salmonella montevideo from wheat contaminated with 10(6) organisms/g to clean wheat. The insects were fed on the contaminated grain for 21 days and were then transferred to clean grain and allowed to feed for 21 days. They were subsequently transferred to two more samples of clean wheat. All species carried S. montevideo into the initial sample of clean wheat but not into a second or third sample. Progeny of the original insects that developed in the contaminated wheat exhibited less ability than the original adults to contaminate clean wheat. Data indicated that few S. montevideo could be carried by the stored-product insects in large masses of grain.     

Quantitative Nasal Culture: a Tool in Antibiotic Research

The use of the quantitative nasal culture was investigated as a means of evaluation of new antimicrobial drugs in man. Cyclacillin was somewhat more active in vitro than penicillin G against penicillin G-resistant organisms. Cyclacillin was highly effective in suppressing staphylococci susceptible to penicillin G in nasal carriers but did not suppress staphylococci resistant to penicillin G. Although in previous studies by others cyclacillin was effective in treating mice infected with penicillin G-resistant staphylococci, in the present studies cyclacillin was not effective in suppressing nasal penicillin G-resistant staphylococci in man at doses which markedly suppressed penicillin G-sensitive organisms.