Characterization of a frequent polymorphism in the coding sequence of the Tp53 gene in colonic cancer patients and a control population

Summary We describe a simple method for characterizing a frequent polymorphism (that subsitutes an arginine for a proline) in the coding sequence of the Tp53 gene in patients with colonic cancer and in a control population. We could find no evidence that this polymorphism is associated with a marked predisposition to colorectal cancer.     

Comparison of transforming growth factor β and a human tumour-derived suppressor factor

Summary Serum-free supernatants from the human melanoma cell line G361 contain a factor that can potently suppress the generation of tumouricidal lymphokine-activated killer (LAK) cells in response to interleukin-2. To characterise the suppressive factor of tumour origin we performed a number of physicochemical and functional comparisons with another immunosuppressive protein, transforming growth factor (TGF). The bioactivity of tumour-derived suppressor factor (TDSF), assayed by suppression of LAK cell generation, was unaffected by a reducing agent but lost when denatured with a chaotropic agent. In contrast, TGF was inactivated by reduction but not denaturation. TDSF lost bioactivity in conditions of pH less than 4, whereas TGF showed no loss of activity. The TDSF moiety has an estimated pI of 4.3 and a molecular mass of 69–87 kDa. This differs from published values of pI 9.5, and 25 kDa molecular mass for TGF. Anti-TGF antiserum reversed the effects of TGF but did not affect the suppression of LAK cell generation caused by TDSF. These findings provide compelling evidence that the TDSF moiety is not TGF, and may be a novel immunoregulatory cytokine.     

Genetic and molecular analysis of spontaneous respiratory deficient (res-) mutants of Escherichia coli K-12

Respiratory deficient (res-) mutants of E. coli are slow growing microcolonial, anaerobic, catalase and benzidine negative strains whose broad phenotypic alteration may result from pleiotropic mutations in genes of the hemin biosynthetic pathway. They are easily recovered from platings of sensitive cells on concentrations of gentamicin higher than the minimal inhibitory concentration. These mutants show a dramatic change in their biochemical diagnostic profile resulting primarily from deficiencies in the active transport mechanisms of the cell. Using well-marked F- and Hfr strains, 157 mutants were analyzed from 3 different parent strains; all but 2 resulted from mutations in 3 loci of the hemin biosynthetic pathway. Of these a marked skew to hemB- mutations was seen, with more than 80% mapping there. The possibility that this hot spot resulted from transpositional activity was tested by Southern hybridization of EcoRI digests of the chromosomal DNA, using as a probe, a 2.8-kb fragment containing the hemB gene. The WT and other hemB+ control strains contained a 14.6-kb fragment. Of 18 hemB strains tested, 14 showed deletion and insertion mutations which fell into four classes based on the variation in the size of the fragment or on the absence of hybridization. The latter resulted from complete deletion of the hemB gene. An increase in fragment size from 1.5-kb to 3.4-kb was observed in some of the strains.     

Cloning of Trametes versicolor Genes Induced by Nitrogen Starvation

We have screened a genomic library of Trametes versicolor for genes whose expression is associated with nitrogen starvation, which has been shown to induce ligninolytic activity. Using two different approaches based on differential expression, we isolated 29 clones. These were shown by restriction mapping and cross-hybridization to code for 11 distinct differentially expressed genes. Northern analysis of the kinetics of expression of these genes revealed that at least four of them have kinetics of induction that parallel kinetics of induction of ligninolytic activity.     

M?ssbauer spectroscopic studies of the cores of human, limpet and bacterial ferritins

Ferritin cores from human spleen, limpet (Patella vulgata) haemolymph and bacterial (Pseudomonas aeruginosa) cells have been investigated using 57Fe M?ssbauer spectroscopy. The M?ssbauer spectra were recorded over a range of temperatures from 1.3 to 78 K, all the spectra are quadrupole-split doublets with similar quadrupole splittings and isomer shifts, characteristic of iron(III), while at sufficiently low temperatures the spectra of all the samples show well-resolved magnetic splitting. At intermediate temperatures, the spectra from the human ferritin exhibit typical superparamagnetic behaviour, while those from the bacterial ferritin show behaviour corresponding to a transition from a magnetically ordered to a paramagnetic state. The spectra from the limpet ferritin show a complex combination of the two effects. The results are discussed in terms of the magnetic behaviour of small particles. The data are consistent with magnetic ordering temperatures of about 3 and 30 K for the bacterial and limpet ferritin cores, respectively, while the data indicate that the magnetic ordering temperature for the human ferritin cores must be above 50 K. These differences are interpreted as being related to different densities of iron in the cores and to variations in the composition of the cores. The human ferritin cores are observed to have a mean superparamagnetic blocking temperature of about 40 K, while that of the limpet ferritin cores is about 25 K. This difference is interpreted as being due not only to different mean numbers of iron atoms in the two types of core but also to the higher degree of crystallinity in the cores of the human ferritin.     

A new species of solanum section geminata (Solanaceae) from western Mexico

Solanum malacothrix S. Knapp is described from the slopes of the Sierra Madre del Sur in the Río Balsas drainage in the state of Guerrero. It is apparently rare, and has been collected only twice. Its relationship to other species in Mexico and northern South America is discussed.     

Effect of an abiotic disturbance on a lotic predator-prey interaction

Summary A model derived from marine research, and recently applied to stream communities, suggests that community structure is more likely to be influenced by predators in benign versus harsh abiotic regimes. Experiments were conducted to determine if increasing the harshness of a particular regime would alter the impact of a stream invertebrate predator on prey densities in field enclosures. Density of a stonefly predator, Kogotus nonus, was varied in containers exposed to low (benign) and high (harsh) levels of fine sediment. As predicted by the model, the harsher regime eliminated predator effects in two of three experiments. In the third experiment, however, high levels of sediment actually enhanced the impact of the predator on the prey community. A consideration of the possible mechanisms underlying this model led to the conclusion that increasing the harshness of a regime can be expected to produce outcomes ranging from elimination to enhancement of predator effects, depending on how the regime is perceived by the predator versus the prey.     

Laboratory studies on salmonella-contaminated cheese involved in a major outbreak of gastroenteritis

Dried biomass of Streptomyces cyaneus NCIB 9616 harvested at 1, 3, 7, 10 and 14 d from a liquid culture was degraded by alkaline methanolysis and the fatty acid methyl esters released examined quantitatively by gas chromatography. Isoprenoid quinones were extracted with petroleum ether and methanolic saline, purified by thin-layer chromatography and quantified by high performance liquid chromatography. Data for each component were plotted against time. The results showed that at the beginning of logarithmic growth there was a small quantitative shift in the fatty acid composition but, the fatty acid profiles remained relatively constant during both the logarithmic and stationary phases of growth. In contrast, the isoprenoid quinone composition depended markedly on the stage of growth. These results indicate that valid comparison of isoprenoid quinone profiles requires that sampling take place at defined stages of the growth cycle.