The rfaD gene codes for ADP-L-glycero-D-mannoheptose-6-epimerase. An enzyme required for lipopolysaccharide core biosynthesis

The rfaD gene product, ADP-L-glycero-D-mannoheptose-6-epimerase, is necessary for the conversion of ADP-D-glycero-D-mannoheptose to ADP-L-glycero-D-mannoheptose. The nucleotide ADP-D-glycero-D-mannoheptose accumulates in rfaD mutant strains. Two chimeric colicin E1 plasmids carrying the coding sequence of the rfaD+ locus have been selected and shown to complement the rfaD phenotype. These clones also result in an amplification of ADP-L-glycero-D-mannoheptose-6-epimerase activity.     

Characterization of the self association of Avian sarcoma virus integrase by analytical ultracentrifugation.

Retroviral integration protein (IN) has been shown to be both necessary and sufficient for the integration of reverse-transcribed retroviral DNA into the host cell DNA. It has been demonstrated that self-assembly of IN is essential for proper function. Analytical ultracentrifugation was used to determine the stoichiometry and free energy of self-association of a full-length IN in various solvents at 23.3 degrees C. Below 8% glycerol, an association stoichiometry of monomer-dimer-tetramer is observed. At salt concentrations above 500 mM, dimer is the dominant species over a wide range of protein concentrations. However, as physiological salt concentrations are approached, tetramer formation is favored. The addition of glycerol to 500 mM NaCl, 20 mM Tris (pH 8.4), 2 mM beta-mercaptoethanol significantly enhances dimer formation with little effect on tetramer formation. Furthermore, as electrostatic shielding is increased by increasing the ionic strength or decreasing the cation size, dimer formation is strengthened while tetramer formation is weakened. Taken together, the data support a model in which dimer formation includes favorable buried surface interactions which are opposed by charge-charge repulsion, while favorable electrostatic interactions contribute significantly to tetramer formation.     

An unusual pontine mass lesion.

A 27-year-old Puerto Rican man presented to Yale-New Haven Hospital with a six-week history of left-sided headache, diplopia, and drooping of the left side of his face. Cerebrospinal fluid examination showed a lymphocytic pleocytosis and a CT scan of the brain revealed an unusual intrapontine mass lesion requiring systemic antifungal therapy. This case emphasizes many of the diagnostic and therapeutic considerations required for effective therapy of fungal disease in the central nervous system.     

Benzene and the risk of non-Hodgkin lymphoma: A review and meta-analysis of the literature

Benzene, an accepted leukemogen, has been suggested to cause other hemato- and lymphopoietic cancers. Here we review the published literature for non-Hodgkin lymphoma (NHL) and occupational exposure to benzene. Six cohorts, sixteen case–control studies and two studies of other designs were identified through keyword searches of bibliographic databases. Twenty-two of twenty-four studies found no association between NHL and ever exposed to benzene compared to never; a random-effects meta-analysis gave a pooled risk estimate of 1.11 (95% confidence interval 0.94–1.30). Our finding of no effect agrees with one of two previous meta-analyses. The other meta-analysis examined if high benzene exposure increased NHL risk but a lack of consistent exposure categories within the same metric should have precluded pooling risks by exposure level. Instead, we reviewed whether dose–response relationships existed. The best available data came from six studies where exposure was estimated from historical measurements and on the whole, no trends in risks of NHL with rising cumulative, average, peak, or duration of benzene exposure were found. NHL is a heterogeneous group of malignancies and although less well-studied, benzene was not associated with any NHL subtype. In conclusion, benzene at either low or high doses does not increase the risk of NHL.     

NMR spectroscopy of 113Cd(II)-substituted gene 32 protein

Gene 32 protein (g32P), the single-stranded DNA binding protein from bacteriophage T4, contains 1 mol of Zn(II)/mol of protein. This intrinsic zinc is retained within the DNA-binding core fragment, g32P-(A+B) (residues 22-253), obtained by limited proteolysis of the intact protein. Ultraviolet circular dichroism provides evidence that Zn(II) binding causes significant changes in the conformation of the peptide chain coupled with alterations in the microenvironments of tryptophan and tyrosine side chains. NMR spectroscopy of the 113Cd(II) derivative of g32P-(A+B) at both 44.4 and 110.9 MHz shows a single 113Cd resonance, delta 637, a chemical shift consistent with coordination to three of the four sulfhydryl groups in the protein. In vitro mutagenesis of Cys166 to Ser166 creates a mutant g32P that still contains 1 Zn(II)/molecule. This mutant protein when substituted with 113Cd(II) shows a 113Cd signal with a delta and a line width the same as those observed for the wild-type protein. Thus, the S-ligands to the metal ion appear to be contributed by Cys77, Cys87, and Cys90. Relaxation data suggest that chemical shift anisotropy is the dominant, but not exclusive, mechanism of relaxation of the 113Cd nucleus in g32P, since a dipolar modulation from ligand protons is observed at 44.4 MHz but not at 110.9 MHz. Complexation of core 113Cd g32P with d(pA)6 or Co(II) g32P with poly(dT) shows only minor perturbation of the NMR signal or d-d electronic transitions, respectively, suggesting that the metal ion in g32P does not add a ligand from the bound DNA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Trophic interactions in soils as they affect energy and nutrient dynamics. IV. Flows of metabolic and biomass carbon

Flows of biomass and respiratory carbon were studied in a series of propylene-oxide sterilized soil microcosms. One-half of the microcosms received three pulsed additions of 200 ppm glucose-carbon to mimic rhizosphere carbon inputs. Biotic variables were: bacteria (Pseudomonas) alone, or amoebae (Acanthamoeba) and nematodes (Mesodiplogaster) singly, or both combined in the presence of bacteria.Over the 24-day experiment, respiration was significantly higher in the microcosms containing the bacterial grazers. Biomass accumulation by amoebae was significantly higher than that by nematodes. The nematodes respired up to 30-fold more CO₂ per unit biomass than did amoebae. Similar amounts of carbon flowed into both respiratory and biomass carbon in microcosms with fauna, compared with the bacteria-alone microcosms. However, partitioning of available carbon by the microfauna varied considerably, with little biomass production and relatively more CO₂-C produced in the nematode-containing microcosms. The amoebae, in contrast, allocated more carbon to tissue production (about 40% assimilation efficiency) and correspondingly less to CO₂.     

Fundamental stimulus for erythropoietin production in the neonatal rat

A mild degree of hemolytic anemia was induced in neonatal rats by a single subcutaneous injection with phenylhydrazine (PHZ). The ability to respond to this challenge was determined by monitoring serum erythropoietin (EP) levels at 6 and 12 hr. At 6 hr after PHZ, EP reached a level of 4.25 ± 1.03 U/ml, and at the 12-hr interval it had increased to 6.12 ± 1.49 U/ml. Based on these data, it is our suggestion that PHZ-induced hemolysis affords an effective stimulus for EP production in the neonatal rodent.