Purification and properties of nuclease SP.

Single-strand-specific nucleases are a diverse and important group of enzymes that are able to cleave a variety of DNA structures present in duplex molecules. Nuclease SP, an enzyme from spinach, has been purified to apparent homogeneity, allowing for the unambiguous characterization of a number of its physical properties as well as its DNA strand cleavage specificities. The effects of ionic strength, pH, divalent metal cations, and temperature on nuclease SP activity have been examined in detail. Nuclease SP was found to be quite thermostable and could be stimulated by Co2+. In addition, the cleavage of UV-damaged and undamaged supercoiled plasmid substrates under a variety of conditions suggests that at least two types of structures are recognized and processed by nuclease SP: UV photoproduct-induced distortions and unwound "nuclease hypersensitive sites". These studies indicate that nuclease SP is functionally related to other single-strand-specific nucleases and is a potential enzymatic tool for probing and manipulating various types of DNA structures.     

Sequence identity between the alpha 2-macroglobulin receptor and low density lipoprotein receptor-related protein suggests that this molecule is a multifunctional receptor.

Ten peptides, derived from human alpha 2-macroglobulin (alpha 2M) receptor by chemical or proteolytic digestion, were sequenced. Comparative analysis revealed that all of the resulting sequences were present within the cDNA-deduced structure of low density lipoprotein receptor-related protein (LRP) (Herz, J., Hamann, U., Rogne, S., Myklebost, O., Gausepohl, H., and Stanley, K. K. (1988) EMBO J. 7, 4119-4127). The findings provide evidence that the alpha 2M receptor and LRP are the same molecule. Further evidence comes from immunoprecipitation experiments using a monoclonal antibody specific for the alpha 2M receptor that show this molecule, like LRP, to contain two polypeptides of approximately 420 and 85 kDa that are noncovalently associated. An additional component of this receptor system is a 39-kDa polypeptide that co-purifies with the alpha 2M receptor during affinity chromatography. Solid phase binding studies reveal that the 39-kDa polypeptide binds with high affinity (Kd = 18 nM) to the 420-kDa component of the alpha 2M receptor. The apparent identity of LRP and the alpha 2M receptor suggests that this molecule is a multifunctional receptor with the capacity to bind diverse biological ligands and highlights a possible relationship between two previously unrelated biological processes, lipid metabolism and proteinase regulation.     

The induction of antigenic changes in a teratocarcinoma stem cell line (F9) by retinoic acid

Treatment of embryonal carcinoma cells F9 with retinoic acid results in the appearance of epithelioid cells resembling endoderm which synthesize basement membrane protein and plasminogen activator. Concomitant with the appearance of these properties of differentiated cells, the epithelial cells cease to express SSEA-1, an antigenic determinant characteristic of teratocarcinoma stem cells and early mouse embryos. Our evidence indicates that the phenotypic changes that accompany retinoic acid treatment of embryonal carcinoma cells are irreversible and a consequence of the differentiation of the cells into endoderm.     

Histone H2B variants from the erythrocytes of an amphibian, a reptile and a bird

Histones H2B have been isolated from the terminally differentiated diploid erythrocytes of three different classes, amphibia (Xenopus laevis), reptilia (Crocodilus niloticus) and aves (Gallus domesticus). Partial amino acid sequences revealed three regions of sequence variation, each variant involving a single amino acid substitution.     

Uncoupler and anaerobic resistant transport of phosphate in Escherichia coli

Active transport of inorganic phosphate into whole cells of a strain (AB3311) derived from $\text{Escherichia coli}$ K12 was found to be partially resistant to 50 μM carbonyl cyanide $\text{m}$-chlorophenyl hydrazone (CCCP), a powerful uncoupler of oxidative phosphorylation. The presence of 10 mM dithiothreitol (DTT) before the addition of CCCP completely prevented the inhibition of phosphate uptake caused by the uncoupler. The addition of DTT to the CCCP-inhibited system restored phosphate uptake to the control rate even when added 5 min after the phosphate transport assay was started. This uncoupler resistant transport is insensitive to anaerobiosis, or the addition of 10 mM KCN which reduces oxygen consumption to less than 1% that of aerobic controls. Additional studies of transport in a mutant (CBT302) deficient in membranebound Ca²⁺-, Mg²⁺-ATPase activity also demonstrated the retention of appreciable inorganic phosphate uptake under anaerobic conditions.     

Adenyl cyclase and cyclic nucleotide phosphodiesterase activities in murine muscular dystrophy.

Adenyl cyclase and cyclic nucleotide phosphodiesterase activities were assayed in homogenates of hind leg skeletal muscle from dystrophic and normal mice. Adenyl cyclase activity was stimulated 2.5 times by epinephrine and 6 times by fluoride over the basal activity in both dystrophic and normal mice. The activity of adenyl cyclase from dystrophic muscle of mice was significantly higher than that of normal mice under all the conditions tested (i.e. basal, epinephrine and fluoride). Cyclic nucleotide phosphodiesterase from skeletal muscle of mice has two Km's (2.1 and 11 mumol/l) which suggests the existence of either two forms of enzyme or a single enzyme with negative cooperativity. The activity of this enzyme was significantly elevated in the skeletal muscle of dystrophic mice compared to the normal controls. The available evidence suggests that the same cyclic nucleotide phosphodiesterase is responsible for the hydrolysis of both cyclic AMP and cyclic GMP.     

HETEROTROPHY OF FOUR MARINE PHYTOPLANKTERS AT LOW SUBSTRATE CONCENTRATIONS1

Three pelagic marine phytoplankters, Coccolithus huxleyi, Skeletonema costatum, and Thalassiosira rotula, and a facultative heterotroph, Cyclotella cryptica, have been exposed to three organic substrates, viz, glucose, acetate, and glutamate, at low concentrations (organic carbon 0.25 mg/liter). Experiments were performed in the dark and light and the net assimilation of substrate was measured by using radiocarbon. The dark uptake of carbon dioxide was also determined, together with photosynthesis at near optimum light intensity. The expected heterotrophy was detected with Cyclotella cryptica. Thalassiosira rotula was found to assimilate glutamate at an appreciable rate. In all cases, however, the short-term uptake of carbon dioxide in the dark was the greatest assimilation rate measured. Values are discussed in relation to their ecological significance and it is concluded that heterotrophic survival of these and probably most other algae in the open ocean would be impossible unless they were in contact with a high concentration of substrate in the form of particulate matter.     

Oncornaviral protein modulation in mouse uterine tissue by estrogen (38467).

Treatment of ovariectomized NIH Swiss mice with estrogens elevated the level of the murine leukemia virus group specific protein and the activity of an RNA-directed DNA polymerase in the uterus. The extent that these markers were raised was dependent on the relative biological potency of the estrogen and on the time interval following treatment. Increases in the levels of both viral marker proteins were evident within 24 hr of treatment and were highest at 48 hr. Subsequently, viral protein levels declined to pretreatment levels.     

Spatiotemporal spread of Plasmodium falciparum mutations for resistance to sulfadoxine-pyrimethamine across Africa, 1990–2020

BackgroundSulfadoxine-pyrimethamine (SP) is recommended in Africa in several antimalarial preventive regimens including Intermittent Preventive Treatment in pregnant women (IPTp), Intermittent Preventive Treatment in infants (IPTi) and Seasonal Malaria Chemoprevention (SMC). The effectiveness of SP-based preventive treatments are threatened in areas where Plasmodium falciparum resistance to SP is high. The prevalence of mutations in the dihydropteroate synthase gene (pfdhps) can be used to monitor SP effectiveness. IPTi-SP is recommended only in areas where the prevalence of the pfdhps540E mutation is below 50%. It has also been suggested that IPTp-SP does not have a protective effect in areas where the pfdhps581G mutation, exceeds 10%. However, pfdhps mutation prevalence data in Africa are extremely heterogenous and scattered, with data completely missing from many areas.Methods and findingsThe WWARN SP Molecular Surveyor database was designed to summarize dihydrofolate reductase (pfdhfr) and pfdhps gene mutation prevalence data. In this paper, pfdhps mutation prevalence data was used to generate continuous spatiotemporal surface maps of the estimated prevalence of the SP resistance markers pfdhps437G, pfdhps540E, and pfdhps581G in Africa from 1990 to 2020 using a geostatistical model, with a Bayesian inference framework to estimate uncertainty. The maps of estimated prevalence show an expansion of the pfdhps437G mutations across the entire continent over the last three decades. The pfdhps540E mutation emerged from limited foci in East Africa to currently exceeding 50% estimated prevalence in most of East and South East Africa. pfdhps540E distribution is expanding at low or moderate prevalence in central Africa and a predicted focus in West Africa. Although the pfdhps581G mutation spread from one focus in East Africa in 2000, to exceeding 10% estimated prevalence in several foci in 2010, the predicted distribution of the marker did not expand in 2020, however our analysis indicated high uncertainty in areas where pfdhps581G is present. Uncertainty was higher in spatial regions where the prevalence of a marker is intermediate or where prevalence is changing over time.ConclusionsThe WWARN SP Molecular Surveyor database and a set of continuous spatiotemporal surface maps were built to provide users with standardized, current information on resistance marker distribution and prevalence estimates. According to the maps, the high prevalence of pfdhps540E mutation was to date restricted to East and South East Africa, which is reassuring for continued use of IPTi and SMC in West Africa, but continuous monitoring is needed as the pfdhps540E distribution is expanding. Several foci where pfdhps581G prevalence exceeded 10% were identified. More data on the pfdhps581G distribution in these areas needs to be collected to guide IPTp-SP recommendations. Prevalence and uncertainty maps can be utilized together to strategically identify sites where increased surveillance can be most informative. This study combines a molecular marker database and predictive modelling to highlight areas of concern, which can be used to support decisions in public health, highlight knowledge gaps in certain regions, and guide future research.