Ability of various alkylating agents to induce adaptive and SOS responses: a study with lacZ fusion

We used alkA'-lacZ' and umuC'-lacZ' fused genes and determined the ability of various alkylating agents to induce adaptive and SOS responses. The degree of induction of expression of these genes was quantitatively measured by a simple colorimetric assay of beta-galactosidase activity. SN1 type methylating agents, such as N-methyl-N'-nitro-N-nitrosoguanidine and N-methyl-N-nitrosourea, were more effective inducers for the alkA than for the umuC system, while SN1 type ethylating agents, such as N-ethyl-N'-nitro-N-nitrosoguanidine and N-ethyl-N-nitrosourea, were more potent inducers for the umuC than for the alkA system. Similar but less striking effects on the two systems were obtained with SN2 type alkylating agents.     

Neurotransmitters in the intestine of the Atlantic cod, Gadus morhua

The effects of the putative neurotransmitters acetylcholine, adrenaline, adenosine, ATP, bombesin, 5-hydroxytryptamine, met-enkephalin, neurotensin, somatostatin, substance P and VIP have been investigated in the perfused intestine of the cod, Gadus morhua. The presence and distribution of the different types of nerves was investigated with immunohistochemistry and Falck-Hillarp fluorescence histochemistry. A spontaneous rhythmic activity of the perfused preparations usually occurred within a few minutes from the start of the experiment. This activity was diminished or abolished by addition of atropine, methysergide or tetrodotoxin to the perfusion fluid. Acetylcholine, 5-hydroxytryptamine or substance P caused a contraction of the intestinal wall. The response to acetylcholine was blocked by atropine but not by tetrodotoxin, while the response to 5-hydroxytryptamine was blocked by methysergide and usually also by tetrodotoxin. This indicates that the effect of acetylcholine is direct on the muscle cells, while the effect of 5-hydroxytryptamine may be at least partly via a second neuron. All adrenergic agonists (adrenaline, isoprenaline and phenylephrine) had a dominating inhibitory effect on the intestine. Experiments with antagonists showed that the inhibition is due to stimulation of both alpha-adrenoceptors and beta-adrenoceptors. ATP, adenosine and somatostatin also caused a relaxation of the intestinal wall, often followed by a contraction. Met-enkephalin produced variable responses, either a relaxation, a contraction or both. Bombesin caused a weak inhibition, if anything. Neurotensin and VIP did not visibly affect the intestinal motility. 5-HT-, substance P- and VIP-like immunoreactivity and catecholamine fluorescence were observed in the myenteric plexus, submucosa and muscle layers in all parts of the intestine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of water flow on transmembrane ionic currents in neurons of Helix pomatia and in squid giant axons

1. The effects of water flow through the membrane produced by an osmotic gradient on the ionic currents in Helix neurons and in squid giant axons were studied. 2. Outward water flow had a marked effect on the ionic currents. 3. Cell volume diminution in hypertonic solution was accompanied by a decrease in the number of functioning ionic channels in the neurons. 4. Decrease of the tonicity of the external 10(-8) M TTX-containing solution leads to a transient recovery of the action potentials of the squid.     

Translation efficiency in humans: tissue specificity,global optimization and differences between developmental stages

Various studies in unicellular and multicellular organisms have shown that codon bias plays a significant role in translation efficiency (TE) by co-adaptation to the tRNA pool. Yet, in humans and other mammals the role of codon bias is still an open question, with contradictory results from different studies. Here we address this question, performing a large-scale tissue-specific analysis of TE in humans, using the tRNA Adaptation Index (tAI) as a direct measure for TE. We find tAI to significantly correlate with expression levels both in tissue-specific and in global expression measures, testifying to the TE of human tissues. Interestingly, we find significantly higher correlations in adult tissues as opposed to fetal tissues, suggesting that the tRNA pool is more adjusted to the adult period. Optimization based analysis suggests that the tRNA pool—codon bias co-adaptation is globally (and not tissue-specific) driven. Additionally, we find that tAI correlates with several measures related to the protein functionally importance, including gene essentiality. Using inferred tissue-specific tRNA pools lead to similar results and shows that tissue-specific genes are more adapted to their tRNA pool than other genes and that related sets of functional gene groups are translated efficiently in each tissue. Similar results are obtained for other mammals. Taken together, these results demonstrate the role of codon bias in TE in humans, and pave the way for future studies of tissue-specific TE in multicellular organisms.     

Identification and purification of overlapping cosmid clones of the region Xq24-qter of human X chromosome using HPLC.

The assembly of a large physical map of genomes requires simultaneous analysis of many cosmid clones for overlapping regions. The search for overlapping regions may be achieved by various means. High-performance liquid chromatography (HPLC) provides an alternative to gel electrophoresis since microgram amounts of each DNA fragment may be collected into individual test tubes for further analysis. HPLC has been used to identify overlapping cosmid clones from a pool of cosmid DNA containing the terminal portion of the long arm of the human X chromosome (Xq24-qter). Among 400 cosmids analyzed, 3 were shown to overlap.     

Transbilayer distribution of bromine in fluid bilayers containing a specifically brominated analogue of dioleoylphosphatidylcholine

We describe in this paper the transbilayer distribution of the bromines of the specifically halogenated phospholipid 1-oleoyl-2-(9,10-dibromostearoyl)-sn-glycero-3- phosphocholine (OBPC). The distribution was determined by X-ray diffraction of oriented multilayers of mixtures of OBPC and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) at 66% relative humidity by the general approach of Franks et al. (1978) [Nature 276, 530-532]. The bromine distribution of OBPC in the fluid L alpha phase is described accurately by a pair of Gaussian functions located 7.97 +/- 0.27 A from the center of the bilayer with l/e half-widths of 4.96 +/- 0.62 A. We find that OBPC bilayers are accurately described as DOPC bilayers with an additional bromine distribution centered at the position of the double bond of DOPC and conclude that OBPC is an excellent structural isomorph for DOPC under the conditions of these experiments. The distribution obtained is the complete and fully resolved transbilayer image of the halogen label because the broad distribution of the bromines is due entirely to thermal disorder and not to experimental limitations [Wiener, M. C., & White, S. H. (1991a) Biophys. J. 59, 162-173]. The observed width of the bromine distribution indicates that virtually all of the hydrocarbon interior is accessible to the bromines. The distance between the bromine/double-bond position and the headgroup phosphate position was determined from one-dimensional Patterson maps and found to be approximately 12 A. The application of accurately determined bromine distributions to the quantitative interpretation of fluorescence quenching experiments is discussed. A method for the self-consistent global analysis of diffraction data from mixtures that permits the use of data sets with different instrumental scale factors is developed in an Appendix.     

Electron paramagnetic resonance study of ferrous cytochrome P-450scc-nitric oxide complexes: effects of cholesterol and its analogues

Electron paramagnetic resonance (EPR) spectra of nitric oxide (NO) complexes of ferrous cytochrome P-450scc were measured at 77 K for the first time without using the rapid-mixing and freeze-quenching technique. Without substrate the EPR spectra were very similar to those of cytochrome P-450cam (from Pseudomonas putida) and cytochrome P-450LM (from rat liver microsomes) with rhombic symmetry; gx = 2.071, gz = 2.001, gy = 1.962, and Az = 2.2 mT for 14NO complexes. Upon addition of substrates [such as cholesterol, 22(S)-hydroxycholesterol, 22(R)-hydroxycholesterol, 25-hydroxycholesterol, and 22-ketocholesterol], the EPR spectra exhibited many variations having rhombic symmetry in the major component and an additional minor component with less rhombic symmetry. Furthermore, addition of 20(S)-hydroxycholesterol caused a striking change in the EPR spectrum. The component with rhombic symmetry disappeared completely, and the component with less rhombic symmetry dominated (gx = 2.027, gz = 2.007, gy = 1.984, and Az = 1.76 mT for 14NO complexes). These observations suggest the existence of the following physiologically important natures: (1) the conformational flexibility of the active site of the enzyme due to the steric interaction between the substrate and the heme-bound ligand molecule and (2) the importance of the hydroxylation of the cholesterol side chain at the 20S position to proceed the side-chain cleavage reaction in cytochrome P-450scc.     

Deuterium isotope effects in norcamphor metabolism by cytochrome P-450cam: kinetic evidence for the two-electron reduction of a high-valent iron-oxo intermediate

The kinetics of NADH consumption, oxygen uptake, and hydrogen peroxide production have been studied for norcamphor metabolism by cytochrome P-450cam. The kinetic deuterium isotope effects on these processes, with specifically deuteriated norcamphor, are 0.77, 1.22, and 1.16, respectively. Steady-state UV-visible spectroscopy indicates that transfer of the second electron to the dioxy ferrous P-450 is the rate-limiting step, as it is when camphor is the substrate. The inverse deuterium isotope effect for NADH consumption is consistent with an isotope-dependent branching between monooxygenase and oxidase activity, where these reactivities differ in their NADH:oxygen stoichiometries. However, no isotope-dependent redistribution of steady-state intermediates was detected by isotopic difference UV-visible spectroscopy in the presence of norcamphor. The kinetic isotope effects and steady-state spectral results suggest that the high-valent iron-oxo hydroxylating intermediate [FeO]3+ is reduced by NADH and the physiological electron-transfer proteins to afford water.     

Clonal populations of the mouse mammary cell line,COMMA-D,which retain capability of morphogenesis in vivo

Summary Clonal populations were isolated from the mouse mammary cell line, COMMA-D, by transfection with a dominant-selectable gene, pSV2Neo, which confers resistance to the antibiotic, G418. Seven of twenty-four clones isolated retained the ability of the parental line to repopulate cleared mammary fat pads in vivo as ductal-alveolar hyperplasias. Two sublines designated CDNR2 and CDNR4 retained hyperplastic growth potential after multiple passages in vitro with low incidence of tumor formation. A third subpopulation, CDNR1, contained a single integration site for the pSV2Neo plasmid indicating a bonafide clonal origin for this subline. CDNR1 cells displayed heterogeneous growth phenotypes in vivo including hyperplasia, adenocarcinoma, and bone formation. Functional differentiation of CDNR1 cells organized as alveolarlike structures in vivo or on floating collagen gels in vitro was observed as determined by immunoperoxidase staining for the milk-specific protein, casein. Overall, the results indicate that a subset of cells from the COMMA-D cell line may be functionally analogous to stem cells existing in the mammary gland. Supported by NCI research grants CA-38650, CA-33369, CA-39017, and CA-25215.