Site-Specific Methylation of Adenine in the Nuclear Genome of a Eucaryote, \u3cem\u3eTetrahymena thermophila\u3c/em\u3e

DNA in the polyploid macronucleus of the ciliated protozoan Tetrahymena thermophila contains the modified base N6-methyladenine. We identified two GATC sites which are methylated in most or all of the 45 copies of the macronuclear genome. One site is 2 kilobases 5\u27 to the histone H4-I gene, and the other is 5 kilobases 3\u27 to the 73-kilodalton heat shock protein gene. These sites are de novo methylated between 10 and 16 h after initiation of conjugation, during macronuclear anlage development. The methylation states of these two GATC sites and four other unmethylated GATC sites do not change in the DNA of cells cultured under conditions which change the activity of the genes, including logarithmic growth, starvation, and heat shock

Competing epidemics on complex networks

Human diseases spread over networks of contacts between individuals and a substantial body of recent research has focused on the dynamics of the spreading process. Here we examine a model of two competing diseases spreading over the same network at the same time, where infection with either disease gives an individual subsequent immunity to both. Using a combination of analytic and numerical methods, we derive the phase diagram of the system and estimates of the expected final numbers of individuals infected with each disease. The system shows an unusual dynamical transition between dominance of one disease and dominance of the other as a function of their relative rates of growth. Close to this transition the final outcomes show strong dependence on stochastic fluctuations in the early stages of growth, dependence that decreases with increasing network size, but does so sufficiently slowly as still to be easily visible in systems with millions or billions of individuals. In most regions of the phase diagram we find that one disease eventually dominates while the other reaches only a vanishing fraction of the network, but the system also displays a significant coexistence regime in which both diseases reach epidemic proportions and infect an extensive fraction of the network.Comment: 14 pages, 5 figure

The frequency of epstein-barr virus infection and associated lymphoproliferative syndrome after transplantation and its manifestations in children

Twenty cases of Epstein-Barr virus (EBV)-associated lymphoproliferative syndrome (LPS), defined by the presence of EBV nuclear antigen and/or EBV DNA in tissues, were diagnosed in 1467 transplant recipients in Pittsburgh from 1981—1985. The frequency of occurrence in pediatric transplant recipients was 4% (10/ 253), while in adults it was 0.8% (10/1214) (P < .0005). The frequency of LPS in adults declined after 1983 coincidental with the introduction of cyclosporine monitoring. However there was no apparent decline of LPS in children. We describe these ten pediatric cases and one additional case of LPS in a child who received her transplant before 1981. The frequency of EBV infection in 92 pediatric liver recipients was 63%. Of these subjects, 49% were sero-negative and 77% of those acquired primary infection. Of 11 cases of pediatric EBV-associated LPS, 10 were in children who had primary infection shortly before or after transplantation. These results reinforce the impor-tance of primary EBV infection in producing LPS, which was previously shown in adults. Children are at greater risk because they are more likely to be seronegative for EBV and to acquire primary infection. Three clinical types of LPS were recognized in children. The first (5 cases) was a self-limited mononucleo-sislike syndrome. The second syndrome (4 cases) began similarly, but then progressed over the next two months to widespread lymphoproliferation in internal organs and death. The third type (2 cases) was an extranodal intestinal monoclonal B cell lymphoma, occurring late after primary infection. © 1988 by The Williams and Wilkins Co

Nickel Isotopic Composition and Nickel/Iron Ratio in the Solar Wind: Results from SOHO/CELIAS/MTOF

Using the Mass Time-of-Flight Spectrometer (MTOF)—part of the Charge, Elements, Isotope Analysis System (CELIAS)—onboard the Solar Heliospheric Observatory (SOHO) spacecraft, we derive the nickel isotopic composition for the isotopes with mass 58, 60 and 62 in the solar wind. In addition we measure the elemental abundance ratio of nickel to iron. We use data accumulated during ten years of SOHO operation to get sufficiently high counting statistics and compare periods of different solar wind velocities. We compare our values with the meteoritic ratios, which are believed to be a reliable reference for the solar system and also for the solar outer convective zone, since neither element is volatile and no isotopic fractionation is expected in meteorites. Meteoritic isotopic abundances agree with the terrestrial values and can thus be considered to be a reliable reference for the solar isotopic composition. The measurements show that the solar wind elemental Ni/Fe-ratio and the isotopic composition of solar wind nickel are consistent with the meteoritic values. This supports the concept that low-FIP elements are fed without relative fractionation into the solar wind. Our result also confirms the absence of substantial isotopic fractionation processes for medium and heavy ions acting in the solar win

Determination of Sulfur Abundance in the Solar Wind

Solar chemical abundances are determined by comparing solar photospheric spectra with synthetic ones obtained for different sets of abundances and physical conditions. Although such inferred results are reliable, they are model dependent. Therefore, one compares them with the values for the local interstellar medium (LISM). The argument is that they must be similar, but even for LISM abundance determinations models play a fundamental role (i.e., temperature fluctuations, clumpiness, photon leaks). There are still two possible comparisons—one with the meteoritic values and the second with solar wind abundances. In this work we derive a first estimation of the solar wind element ratios of sulfur relative to calcium and magnesium, two neighboring low-FIP elements, using 10 years of CELIAS/MTOF data. We compare the sulfur abundance with the abundance determined from spectroscopic observations and from solar energetic particles. Sulfur is a moderately volatile element, hence, meteoritic sulfur may be depleted relative to non-volatile elements, if compared to its original solar system valu

Disseminated Toxoplasmosis in a Patient with Non-Hodgkin Lymphoma

Abstract : Toxoplasmosis is a well-recognized opportunistic disease in HIV-infected individuals that is caused by the reactivation of a previous infection, primarily in the central nervous system, during profound immunodeficiency. Toxoplasmosis has been described more rarely in patients with cancer and chemotherapy. We report a case of a patient with a history of chemotherapy for non-Hodgkin lymphoma who developed pain and progressive paresthesia of the right arm 6 weeks after remission. Relapsing lymphoma was suspected, and steroid and radiation treatment were initiated, but the patient died 5 days later due to multiple organ failure. Autopsy revealed disseminated toxoplasmosis. This case illustrates that toxoplasmosis should be suspected in patients with neoplastic disease, especially lymphomas, who present with unexplained neurologic, pulmonary, or febrile symptoms during or after chemotherap