Identification of a DNA nonhomologous end-joining complex in bacteria

In eukaryotic cells, double-strand breaks (DSBs) in DNA are generally repaired by the pathway of homologous recombination or by DNA nonhomologous end joining (NHEJ). Both pathways have been highly conserved throughout eukaryotic evolution, but no equivalent NHEJ system has been identified in prokaryotes. The NHEJ pathway requires a DNA end-binding component called Ku. We have identified bacterial Ku homologs and show that these proteins retain the biochemical characteristics of the eukaryotic Ku heterodimer. Furthermore, we show that bacterial Ku specifically recruits DNA ligase to DNA ends and stimulates DNA ligation. Loss of these proteins leads to hypersensitivity to ionizing radiation in Bacillus subtilis. These data provide evidence that many bacteria possess a DNA DSB repair apparatus that shares many features with the NHEJ system of eukarya and suggest that this DNA repair pathway arose before the prokaryotic and eukaryotic lineages diverged.     

Mississippi deltaic wetland survival: sedimentation versus coastal submergence

Seasonal sedimentation, measured with the aid of artificial marker horizons, was markedly different in deteriorating as compared with stable marshes in the Mississippi River deltaic plain. Deteriorating marshes receive most sediment during storm events, whereas stable marshes receive substantial amounts of sediments during the spring river flood. The deteriorating marshes are accreting at a faster rate (1.5 centimeters per year at streamside, 0.9 centimeter per year at inland areas) than the stable marshes (1.3 centimeters per year at streamside, 0.6 centimeter per year at inland areas). However, relative to local apparent sea-level rise as measured by tide gauges in each area, the deteriorating marshes are not maintaining their intertidal elevation as well as the stable marshes. These results indicate the importance of considering accretion relative to submergence.     

Minimizing bias in a case-control study of farm injury

We report on our strategies to minimize bias in the FIRM study, a prospective case-control study of risk factors for serious farmwork-related injury. The study base is adult males working on farms in the catchment regions of 14 larger regional hospitals in one Australian state. Cases are identified on presentation to the emergency departments, while age-matched controls are recruited via random telephone survey. Eligibility criteria for cases include a maximum abbreviated injury severity score of at least 2, to minimize the potential for selection bias against those with less severe injuries treated outside the hospital system. An audit at one hospital showed that 93% of eligible patients identified in the electronic surveillance system had been approached regarding participation. Results to date show that 38% of those approached decline to have their contact details made available to researchers. Those who decline are asked to complete two key questions to enable comparison with those who participate. Control recruitment relies on telephoning regional households until an individual from the study base, satisfying the matching criteria, is identified. This process minimizes the potential for selecting against farm workers who may live off-farm. Ninety-four percent of age-matched eligible controls have participated to date. We are testing a dynamic pool of individuals identified as study base members but not matched on the first call to determine its effect on the probabilities of selection. Our strategies appear to be minimizing detection, selection, and response bias, thereby enhancing the validity of the study results.     

Feedback of 17 beta-estradiol on secretion of luteinizing hormone during different seasons of the year

The working hypothesis was that the amount of increase in secretion of luteinizing hormone (LH) that results from positive feedback of 17 beta-estradiol (E2) is dependent on season of the year in mature bovine females. Seven beef cows, ovariectomized approximately 2 mo before the initiation of the experiment, were used in the initial year (1983) of the study. Three of the ovariectomized cows (OVX-E2) received an sc E2 implant, which provided low circulating levels of E2. The remaining four cows (OVX) were not implanted. Blood samples were collected serially (at 10-min intervals for 6 h) at each spring and fall equinox and at each summer and winter solstice. This protocol was replicated with a different group of cows in 1985 (OVX-E2, n = 4; OVX, n = 6). Concentration of LH in blood serum was quantified in all samples. Concentration of E2 in blood serum was measured in pools of samples from each serial blood collection. Concentrations of E2 were higher (P less than .05) in the implanted cows. Mean concentration of LH and amplitude of pulses of LH were higher (P less than .05) at each season of the year in cows that were ovariectomized and implanted with E2 than in cows that were ovariectomized and did not receive E2. An effect of season of the year on mean concentration of LH was detected (P less than .01). No influence of season or E2 was detected for frequency of pulses of LH. There was no significant treatment X season interaction.(ABSTRACT TRUNCATED AT 250 WORDS)