Production of the mouse mammary tumor virus in cultures of BALB/cfC3H strain

The mouse mammary tumor virus (MTV) reproduces by a budding mechanism at the cell membrane of mouse mammary epithelial cells. In tissue culture, the tumor cells release their virions in the culture supernatant from which they can be removed by high speed centrifugation. Mammary tumor cells from the RIII, GR, and A strains of mice generally produce yields of virus which decrease after a few months. Cells derived from a spontaneous mammary tumor in a BALB/cfC3H mouse have shown the capability to shed relatively large amounts of virus continuously. A quantitative estimation by membrane immunofluorescence of the number of virus producing cells in one-year-old cultures revealed the presence of viral antigen on 80 to 90% of the cells; by comparison, cultures from other mouse strains had a ratio of only 10 to 15% virus producing cells. High speed centrifugation pellets obtained from 50 ml culture supernatant provided large amounts of mature virus particles which have been characterized by electron microscopy.     

Quenching de la chlorophylle in vivo par le m-dinitrobenzene

The quenching of fluorescence and inhibition of photochemical activities by m-dinitrobenzene have been studied in unicellular algae and chloroplasts.The complementary area $\text{S(=}\text{∫}\text{0}\text{∞}\text{(Δφ}{}_{\mathrm{<mtext>M</mtext>}}\text{?Δφ)}\text{d}\text{t)}$ is decreased in the same fashion as the maximum amplitude of the variable fluorescence Δφ_M, suggesting the invariance of S properly normalized by Δφ_M. A photochemical type inhibition for all photochemical activities (oxygen evolution, Photoreaction II and I) is observed in a concentration range higher than that required to quench Δφ_M. The ratio of the photochemical rate in limiting light to the O₂ burst elicited by a flash is constant whatever the level of inhibition. The pattern of oscillation of O₂ burst during a sequence of flashes is also unmodified, the amplitude only being decreased.In order to explain these results, it is assumed that dinitrobenzene (DNB) has a quenching effect both on the center-chlorophyll and the collector-chlorophyll of the System II photosynthetic units; when the external quencher is only acting on the collector, the trapping efficiency for the center is unmodified, but, when the center is turned into its inactive form by the photochemical reaction, the fluorescence of the collector is quenched. It is shown that the rule of invariance of the normalized complementary area applies to this type of quenching; accordingly, the zero level of the System II fluorescence, within the constant part, (cf. Lavorel, J. et Joliot, P. (1972) Biophys. J. 12, 815–831) should lie close to the 0 level (dark-adapted state).     

Inbreeding in recessive diseases

Summary The consanguinity of parents (born in France) of individuals who have a recessive disease has been studied. The frequency of first cousin marriages is less than 0.2% in the general French population. Among the parents of affected individuals the following frequencies of first cousin matings were observed:cystic fibrosis: 1.4%cystinosis: 7.1%nephronophtisis: 5.6%spinal muscular atrophy: 4.5%albinsism: 5.0%achromatopsia: 12.5%(Albinism and spinal muscular atrophy are heterogeneous conditions). The increase in the frequency of first cousin marriages relative to that of the general population is much greater, as expected, in cystinosis, which is a rare disease, than in cystic fibrosis, which is the most frequent recessive disorder in France.Inbreeding in cystinosis and cystic fibrosis was also studied by computing the distance between parental birth places. This distance is smaller in cystinosis than in cystic fibrosis.     

Kinetics of chlorophyll fluorescence at 77 K in Chlorella and chloroplasts. Effects of CCCP,ferricyanide and DCMU

The kinetics of chlorophyll fluorescence at 77 K were studied in Chlorella cells and spinach chloroplasts.During a first illumination, the rise is polyphasic with at least three phases. The slowest one is irreversible and corresponds to the cytochrome oxidation.The dark regeneration of half the variable fluorescence is biphasic, the fast phase being inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) both in Chlorella and chloroplasts.The fluorescence rise during a second illumination is still biphasic.Carbonyl cyanide m-chlorophenylhydrazone (CCCP) slows down the fluorescence rise in Chlorella but has no effect on the dark regeneration. It does not affect the fluorescence of chloroplasts.Ferricyanide which oxidizes cytochrome b-559 at room temperature produces a quenching of the variable fluorescence and an acceleration of the fluorescence rise during the first illumination.Our results fit the idea of the heterogeneity of the Photosystem II centers at low temperature.     

Type IV pilus biogenesis in Neisseria meningitidis: PilW is involved in a step occurring after pilus assembly, essential for fibre stability and function

Type IV pili (Tfp) play a critical role in the pathogenic lifestyle of Neisseria meningitidis and N. gonorrhoeae, notably by facilitating bacterial attachment to human cells, but our understanding of their biogenesis, during which the fibres are assembled in the periplasm, then emerge onto the cell surface and are stabilized, remains fragmentary. We therefore sought to identify the genes required for Tfp formation in N. meningitidis by screening a genome-wide collection of mutants for those that were unable to form aggregates, another phenotype mediated by these organelles. Fifteen proteins, of which only seven were previously characterized, were found to be essential for Tfp biogenesis. One novel component, named PilW, was studied in more detail. We found that PilW is an outer-membrane protein necessary for the stabilization of the fibres but not for their assembly or surface localization, because Tfp could be restored on the surface in a pilW mutant by a mutation in the twitching motility gene pilT. However, Tfp-linked properties, including adherence to human cells, were not restored in a pilW/T mutant, which suggests that PilW is also essential for the functionality of the fibres. Together with the finding that PilW is important for the stability of PilQ multimers, our results extend the current model for Tfp biogenesis by suggesting that a multiprotein machinery in the outer-membrane is involved in the terminal stage of Tfp biogenesis during which growing fibres are not only stabilized, but also become perfectly functional.