The central role of protein S12 in organizing the structure of the decoding site of the ribosome

The ribosome decodes mRNA by monitoring the geometry of codon–anticodon base-pairing using a set of universally conserved 16S rRNA nucleotides within the conformationally dynamic decoding site. By applying single-molecule FRET and X-ray crystallography, we have determined that conditional-lethal, streptomycin-dependence mutations in ribosomal protein S12 interfere with tRNA selection by allowing conformational distortions of the decoding site that impair GTPase activation of EF-Tu during the tRNA selection process. Distortions in the decoding site are reversed by streptomycin or by a second-site suppressor mutation in 16S rRNA. These observations encourage a refinement of the current model for decoding, wherein ribosomal protein S12 and the decoding site collaborate to optimize codon recognition and substrate discrimination during the early stages of the tRNA selection process.     

Ascorbic acid enhancement of organogenesis in tobacco callus

The effect of ascorbic acid on growth and shoot formation in callus cultures of tobacco (Nicotiana tabacum L.) was investigated, using young (4–12 subcultures) and old (more than 30 subcultures) tissue. It was found that ascorbate, at levels of 4–8×10^-4M, enhanced shoot formation in both young and old callus. Treatment with ascorbate also speeded up the shoot-forming process. In addition, ascorbate completely reversed the inhibition of shoot formation by gibberellic acid in young callus, but was less effective in old callus.     

Effects of AeDNV infection on Aedes aegypti lifespan and reproduction

The effects of Aedes Densovirus (AeDNV) infections on survival, fertility, fecundity and vertical transmission in Aedes aegypti (Diptera: Culicidae) were measured in laboratories in Kiev, Ukraine and Colorado, USA and incorporated into a predictive model of the effects of AeDNV on vector capacity. Adult lifespan and daily survival were reduced in AeDNV infected mosquitoes. This effect was dependent on the dose of the virus. Infected females had decreased fecundity. The oviposition rate was less in infected females and the hatch rate declined in eggs laid by infected females. The amounts of AeDNV in infected females and the infection rate of their offspring were measured with real-time PCR. The average filial transmission rate was 70% and larval infection rates from infected females varied between 42 and 62%. Vertically infected larvae, and individual eggs contained 1 × 10⁵ AeDNV genome equivalents (geq). Modeling the effects of AeDNV infection on Ae. aegypti populations suggested a large decrease in the numbers of eggs, larvae, pupae, and adults arising from infected mothers and suggested that AeDNV treatment of larvae could cause up to a 76% reduction of infectious mosquito days.     

A Simple and Inexpensive Method for Determining Cold Sensitivity and Adaptation in Mice

Cold hypersensitivity is a serious clinical problem, affecting a broad subset of patients and causing significant decreases in quality of life. The cold plantar assay allows the objective and inexpensive assessment of cold sensitivity in mice, and can quantify both analgesia and hypersensitivity. Mice are acclimated on a glass plate, and a compressed dry ice pellet is held against the glass surface underneath the hindpaw. The latency to withdrawal from the cooling glass is used as a measure of cold sensitivity.Cold sensation is also important for survival in regions with seasonal temperature shifts, and in order to maintain sensitivity animals must be able to adjust their thermal response thresholds to match the ambient temperature. The Cold Plantar Assay (CPA) also allows the study of adaptation to changes in ambient temperature by testing the cold sensitivity of mice at temperatures ranging from 30 °C to 5 °C. Mice are acclimated as described above, but the glass plate is cooled to the desired starting temperature using aluminum boxes (or aluminum foil packets) filled with hot water, wet ice, or dry ice. The temperature of the plate is measured at the center using a filament T-type thermocouple probe. Once the plate has reached the desired starting temperature, the animals are tested as described above.This assay allows testing of mice at temperatures ranging from innocuous to noxious. The CPA yields unambiguous and consistent behavioral responses in uninjured mice and can be used to quantify both hypersensitivity and analgesia. This protocol describes how to use the CPA to measure cold hypersensitivity, analgesia, and adaptation in mice.     

Effects of Polyphosphate Additives on Campylobacter Survival in Processed Chicken Exudates

Campylobacter spp. are responsible for a large number of the bacterial food poisoning cases worldwide. Despite being sensitive to oxygen and nutritionally fastidious, Campylobacter spp. are able to survive in food processing environments and reach consumers in sufficient numbers to cause disease. To investigate Campylobacter persistence on processed chicken, exudates from chickens produced for consumer sale were collected and sterilized. Two types of exudates from chicken products were collected: enhanced, where a marinade was added to the chickens during processing, and nonenhanced, where no additives were added during processing. Exudates from enhanced chicken products examined in this study contained a mixture of polyphosphates. Exudate samples were inoculated with Campylobacter jejuni or Campylobacter coli strains and incubated under a range of environmental conditions, and viable bacteria present in the resultant cultures were enumerated. When incubated at 42°C in a microaerobic environment, exudates from enhanced chicken products resulted in increased survival of C. jejuni and C. coli compared with that in nonenhanced exudates in the range of <1 to >4 log CFU/ml. Under more relevant food storage conditions (4°C and normal atmosphere), the exudates from enhanced chicken products also demonstrated improved Campylobacter survival compared with that in nonenhanced exudates. Polyphosphates present in the enhanced exudates were determined to be largely responsible for the improved survival observed when the two types of exudates were compared. Therefore, polyphosphates used to enhance chicken quality aid in sustaining the numbers of Campylobacter bacteria, increasing the opportunity for disease via cross-contamination or improperly cooked poultry.Campylobacter species are the major causative agent of food-borne gastrointestinal bacterial infections in the developed world (6, 11, 21). Poultry products are a major source for the introduction of Campylobacter into the food supply (15, 16). Improperly cooked poultry and cross-contamination of other foods by raw poultry are common methods for transmission of Campylobacter to humans (5). However, Campylobacter spp. are nutritionally fastidious organisms that are sensitive to the oxygen levels present in a normal environment (O₂ = 20.9%) (21). Therefore, Campylobacter appears an unlikely candidate to persist within poultry processing and storage environments at levels sufficient to cause human disease. This conundrum directly leads to a question: what then are the elements that contribute to the ability of Campylobacter to survive through poultry processing and cold storage?To investigate this question, a food-relevant environment consisting of chicken weepage or exudate can be used to perform survival experiments on Campylobacter species. Strains of Campylobacter jejuni and Campylobacter coli were used for the survival studies since these two species are responsible for the vast majority of human cases of campylobacteriosis (20, 28). Chicken exudate is the fluid that seeps out from processed poultry carcasses and is often found to be contaminated with considerable numbers of Campylobacter bacteria. It is comprised of water, blood, fats, and other materials added to the poultry during processing. Sterilized poultry exudates make for a convenient experimental material that is also relevant to the conditions which Campylobacter will experience as a contaminant of processed poultry (2, 3). Two different types of chicken exudates were collected from commercial producers, one from chickens processed without additives (nonenhanced) and the other from chickens that were treated with a commercial marinade to increase the quality and appeal of the meat at market (enhanced). The commercial poultry marinades contain a significant amount of polyphosphate additives. Polyphosphates comprise a group of food additives that are utilized within poultry processing to enhance the moisture absorbance, color, and flavor and to reduce product shrinkage of poultry (24, 29-32). Polyphosphates have also been shown to have an antimicrobial effect on several different bacterial species (8, 10, 12). The goal of the research was to determine if polyphosphates contribute to the ability of Campylobacter to survive and persist through the supply chain, thus directly increasing the opportunity for Campylobacter-mediated food poisoning of consumers.     

Expression, Isolation, and Crystallization of the Catalytic Domain of CopB, a Putative Copper Transporting ATPase from the Thermoacidophilic Archaeon Sulfolobus solfataricus

The P-type CPX-ATPases are responsible for the transport of heavy metal ions in archaea, bacteria, and eukaryotes. We have chosen one of the two CPX-ATPases of the thermophile Sulfolobus solfataricus, CopB (= SSO2896) for the investigation of the molecular mechanism of this integral membrane protein. We recombinately expressed three different soluble domains of this protein (named CopB-A, CopB-B, and CopB-C) in Escherichia coli and purified them to homogeneity. 3D crystals of CopB-B, the 29 kDa catalytic ATP binding/phosphorylation domain were produced, which diffracted to a resolution of 2.2 A. CopB-B has heavy metal stimulated phosphatase activity, which was half maximal in the presence of 80 microM Cu2+. The protein forms a phosphorylated intermediate with the substrate gamma-(32P)-ATP. No specific activation of the polypeptide was observed, when CopB-B phosphatase activity was tested in the presence of the purified CopB-C and CopB-A proteins, which provide the cation binding and the phosphatase domains. We conclude that CopB is a putatively copper translocating ATPase, in which structural elements integrally located in the membrane are required for full, coordinated activation of the catalytic ATP binding domain.