Effect of dark repair on ultraviolet sensitivity of bacteriophage-infected bacteria

Feiner, R. R. (Columbia University, New York, N.Y.), and R. F. Hill. Effect of dark repair on ultraviolet sensitivity of bacteriophage-infected bacteria. J. Bacteriol. 91:1239-1247. 1966.-Changes in ultraviolet (UV) sensitivity of phage-host complexes during phage development have been studied for the following systems: T1 and Escherichia coli B, T1 and E. coli K-12S, lambda and E. coli K-12S. Complexes were formed with bacterial strains differing in ability to dark-repair UV damage to deoxyribonucleic acid and, after irradiation, were plated on bacteria differing similarly. In the first half of the latent period, the resistance of complexes formed with nonrepairing bacteria increased considerably; with T1 and E. coli B hcr(-), in 4 min the resistance became the same as that of complexes formed with repairing bacteria. The repair ability of plating bacteria affected survival curves only upon irradiation in the second half of the latent period after mature phages were present in the initial complex. Use of nonrepairing bacteria both for initial infection and for plating of late complexes resulted in a series of survival curves showing for all three systems the same pattern of change originally reported for T2-E. coli B complexes. Thus, a hitherto unexplained difference between radiation survival curves for T-even and T-odd phages seems due to repair of T-odd phages by the host.     

Computerized matching of relevés and association tables,with an application to the British National Vegetation Classification

When a new relevé is to be assigned to a pre-existing type, its composition is compared with an association table. Bayesian inference may seem a good way to make the comparison, but presents difficulties. In an alternative approach, three indices of goodness-of-fit are proposed. Compositional satisfaction is a measure of how well the species composition of the relevé fits the constancy classes in the table; it is a minor modification of the Czekanowski coefficient of similarity between observed and expected numbers of species in each constancy class. Dominance satisfaction is a modification of the Czekanowski similarity between the relevé and cover values that might be expected from the association table. Dominance constancy is a weighted mean of the constancy class of the four most abundant species in the relevé. A computer program, TABLEFIT, combines them into a single index. It has been tested on British mire vegetation.     

Supplemental oxygen reduces right ventricular hypertrophy in monocrotaline-injected rats

We evaluated the possible contributory role of hypoxia in the development of monocrotaline-induced pulmonary hypertension. Male Sprague-Dawley rats were injected subcutaneously with monocrotaline (60 mg/kg) or saline in controls and were kept in oxygen-enriched (inspired O2 fraction of 0.35) or compressed air chambers. After 21 days, rats were anesthetized while spontaneously breathing room air, hemodynamic parameters and arterial blood gases were measured, and animals were killed. Right ventricular peak systolic pressures (RVPP), right ventricular-to-left ventricular plus septal weight ratios (RV/LV + S), hematocrits, lung dry weight-to-body weight ratios, and medial thickness of pulmonary arteries were significantly reduced in monocrotaline-injected rats exposed to mild hyperoxia compared with air. The air-exposed monocrotaline-injected rats had significantly more arterial hypoxemia than the other groups, and mild hyperoxia had no effect on any of the measured variables in saline-injected rats. To determine whether the effects of mild hyperoxia occurred early or late after monocrotaline injection, we moved separate groups of rats from air to mild hyperoxia and vice versa 10 days after monocrotaline injection. After 21 days, significant reductions in RVPP and RV/LV + S occurred only in rats exposed to mild hyperoxia during the latter 11 days after injection. Our findings suggest that hypoxia contributes to the development of pulmonary hypertension relatively late after monocrotaline injection in rats but that it does not influence the early injury.     

Sewall Wright and quantitative genetics

Some aspects of Wright's great contribution to quantitative genetics and animal breeding are reviewed in relation to current research and practice. Particular aspects discussed are as follows: the utility of his definition of inbreeding coefficient in terms of the correlation of uniting gametes; the maintenance of genetic variation in the optimum model; the inter-relations between past and present animal-breeding practice and the shifting-balance theory of evolution.     

Ras interaction with the GTPase-activating protein (GAP)

Biologically active forms of Ras complexed to GTP can bind to the GTPase-activating protein (GAP), which has been implicated as possible target of Ras in mammalian cells. In order to study the structural features of Ras required for this interaction, we have evaluated a series of mutant ras proteins for the ability to bind GAP and a series of Ras peptides for the ability to interfere with this interaction. Point mutations in the putative effector region of Ras (residues 32-40) that inhibit biological activity also impair Ras binding to GAP. An apparent exception is the Thr to Ser substitution at residue 35; [Ser-35]Ras binds to GAP as effectively as wild-type Ras even though this mutant is biologically weak in both mammalian and S. cerevisiae cells. In vitro, [Ser-35]Ras can also efficiently stimulate the S. cerevisiae target of Ras, adenylyl cyclase, indicating that other factors may influence Ras/protein interactions in vivo. Peptides having Ras residues 17-44 and 17-32 competed with the binding of Ras to E. coli-expressed GAP with IC50 values of 2.4 and 0.9 microM, respectively, whereas Ras peptide 17-26 was without effect up to 400 microM. A related peptide from the yeast GTP-binding protein YPT1 analogous to Ras peptide 17-32 competed with an IC50 value of 19 microM even though the YPT1 protein itself is unable to bind to GAP. These results suggest that determinants within Ras peptide 17-32 may be important for Ras binding to GAP.     

Investigation of the regulation of pigmentation in alpha-melanocyte-stimulating hormone responsive and unresponsive cultured B16 melanoma cells

In vitro melanocyte-stimulating hormone (MSH) stimulates melanogenesis in some, but not all, melanocytes and melanoma cells. In an attempt to explain this variation in response to alpha MSH, we examined cyclic adenosine monophosphate (cAMP) accumulation, tyrosinase activity, and melanin production in primary (1 degree) murine B16 melanoma cells and in two B16 cell lines (B16 F1 and B16 F10) that are known to respond to alpha MSH. In vivo all three B16 melanoma cell types produced pigmented tumours. In vitro alpha MSH increased tyrosinase activity and melanin content in the F1 and F10 cells but not in the B16 1 degree cells. alpha MSH, however, increased cAMP production in all three cell types, confirming that the inability of B16 1 degree cells to produce melanin in response to alpha MSH is not due to a lack of alpha MSH receptors or cAMP response to alpha MSH. Further, we present evidence for a separate pathway of melanogenesis that is independent of cAMP as calmodulin antagonists, which do not elevate cAMP, increased tyrosinase activity, and melanin production in both 1 degree and F1 cells.     

Lipoxygenase and cyclooxygenase blockade by BW755C does not prevent the secondary phase of septic pulmonary hypertension

The infusion of Group B beta hemolytic streptococci (GBS) in newborn animals generates a dual phase pulmonary hypertensive response. The initial, acute phase responds to cyclooxygenase or thromboxane inhibition, and appears to be thromboxane mediated. The second phase is characterized by a more moderate rise in pulmonary vascular resistance, accompanied by an increase in microvascular permeability. It has been speculated that this phase may be leukotriene mediated. In an attempt to clarify this, we have studied and compared the effects of the thromboxane synthetase inhibitor, Dazmegrel (DAZ), and the combined cyclooxygenase/lipoxygenase inhibitor, BW755C, on the cardiopulmonary hemodynamics of the secondary phase of GBS induced pulmonary hypertension in newborn piglets. Ten piglets were infused with GBS, and all animals developed a significant increase in pulmonary artery pressure (to 39 +/- 5 and 36 +/- 5 mmHg for DAZ and BW755C animals respectively). After one hour of GBS, either DAZ or BW755C was administered. Data were collected for another two hours following drug administration. GBS infusion was continued throughout. Both DAZ and BW755C were associated with transient, acute reductions in pulmonary artery pressure (to 22 +/- 5 and 22 +/- 8 mmHg, respectively). However, after 60 minutes, PAP again began to rise in both groups (PAP 30 +/- 5 and 30 +/- 11 mmHg respectively by 240 minutes). There were no differences between the groups at any time. These data do not support a significant role for lipoxygenase products in mediating the secondary phase of septic pulmonary hypertension.     

The calcium-binding site of clathrin light chains

Clathrin light chains are calcium-binding proteins (Mooibroek, M. J., Michiel, D. F., and Wang, J. H. (1987) J. Biol. Chem. 262, 25-28) and clathrin assembly can be modulated by calcium in vitro. Thus, intracellular calcium may play a regulatory role in the function of clathrin-coated vesicles. The structural basis for calcium's influence on clathrin-mediated processes has been defined using recombinant deletion mutants and isolated fragments of the light chains. A single calcium-binding site, formed by residues 85-96, is present in both mammalian light chains (LCa and LCb) and in the single yeast light chain. This sequence has structural similarity to the calcium-binding EF-hand loops of calmodulin and related proteins. In mammalian light chains, the calcium-binding sequence is flanked by domains that regulate clathrin assembly and disassembly.     

Postnatal Development of a Granule Cell-Enriched, Neurone-Specific Glycoprotein, gp50, in Normal and Thyroid-Deficient Rats

Glycoprotein gp50 is a neurone-specific, granule cell-enriched glycoprotein that is also a major component of isolated synaptic membranes. Here, we describe the use of a monoclonal antibody, mab SM gp50, to study the postnatal development of gp50 in the brain of normal and thyroid-deficient rats. Radioimmunoassay, enzyme-linked immunosorbent assay, and Western blotting show that gp50 is not detectable in brain until postnatal day 4 (P4) in both forebrain and cerebellum. In forebrain, the rate of increase of gp50 levels is maximal between P12 and P20. It is somewhat later in cerebellum, where peak levels are attained between P30 and P35. Immunocytochemical studies show little detectable gp50-like immunoreactivity before P16, and the staining is still weak, relative to adult tissue, at P25. The intense staining of the granule cell layer characteristic of adult cerebellum predominantly appears after P25. Development of gp50 is severely retarded in the cerebellum of thyroid-deficient rats, particularly during the second and third postnatal weeks. However, by the fourth postnatal week, gp50 levels in normal and hypothyroid animals are comparable. The results indicate that significant alterations in the pattern of gp50 expression continue to occur at a late stage of cerebellar development. In particular, the increase in immunocytochemical staining of the granule cells after P25 is striking in that by this time most major events associated with cerebellar development are essentially complete.