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  • State transitions in the cyanobacterium Synechococcus elongatus 7942 involve reversible quenching of the photosystem II core.

    15 juin, par Choubeh RR, Wientjes E, Struik PC, Kirilovsky D, van Amerongen H
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    State transitions in the cyanobacterium Synechococcus elongatus 7942 involve reversible quenching of the photosystem II core.

    Biochim Biophys Acta. 2018 Jun 11;:

    Authors: Choubeh RR, Wientjes E, Struik PC, Kirilovsky D, van Amerongen H

    Abstract
    Cyanobacteria use chlorophyll and phycobiliproteins to harvest light. The resulting excitation energy is delivered to reaction centers (RCs), where photochemistry starts. The relative amounts of excitation energy arriving at the RCs of photosystem I (PSI) and II (PSII) depend on the spectral composition of the light. To balance the excitations in both photosystems, cyanobacteria perform state transitions to equilibrate the excitation energy. They go to state I if PSI is preferentially excited, for example after illumination with blue light (light I), and to state II after illumination with green-orange light (light II) or after dark adaptation. In this study, we performed 77-K time-resolved fluorescence spectroscopy on wild-type Synechococcus elongatus 7942 cells to measure how state transitions affect excitation energy transfer to PSI and PSII in different light conditions and to test the various models that have been proposed in literature. The time-resolved spectra show that the PSII core is quenched in state II and that this is not due to a change in excitation energy transfer from PSII to PSI (spill-over), either direct or indirect via phycobilisomes.

    PMID: 29902424 [PubMed - as supplied by publisher]

  • The Bacteriophage Head-to-Tail Interface.

    15 juin, par Tavares P
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    The Bacteriophage Head-to-Tail Interface.

    Subcell Biochem. 2018;88:305-328

    Authors: Tavares P

    Abstract
    Many icosahedral viruses use a specialized portal vertex for genome encapsidation in the viral capsid (or head). This structure then controls release of the viral genetic information to the host cell at the beginning of infection. In tailed bacteriophages, the portal system is connected to a tail device that delivers their genome to the bacterial cytoplasm. The head-to-tail interface is a multiprotein complex that locks the viral DNA inside the phage capsid correctly positioned for egress and that controls its ejection when the viral particle interacts with the host cell receptor. Here we review the molecular mechanisms how this interface is assembled and how it carries out those two critical steps in the life cycle of tailed phages.

    PMID: 29900503 [PubMed - in process]

  • Replication Fork Breakage and Restart in Escherichia coli.

    15 juin, par Michel B, Sinha AK, Leach DRF
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    Replication Fork Breakage and Restart in Escherichia coli.

    Microbiol Mol Biol Rev. 2018 Sep;82(3):

    Authors: Michel B, Sinha AK, Leach DRF

    Abstract
    In all organisms, replication impairments are an important source of genome rearrangements, mainly because of the formation of double-stranded DNA (dsDNA) ends at inactivated replication forks. Three reactions for the formation of dsDNA ends at replication forks were originally described for Escherichia coli and became seminal models for all organisms: the encounter of replication forks with preexisting single-stranded DNA (ssDNA) interruptions, replication fork reversal, and head-to-tail collisions of successive replication rounds. Here, we first review the experimental evidence that now allows us to know when, where, and how these three different reactions occur in E. coli. Next, we recall our recent studies showing that in wild-type E. coli, spontaneous replication fork breakage occurs in 18% of cells at each generation. We propose that it results from the replication of preexisting nicks or gaps, since it does not involve replication fork reversal or head-to-tail fork collisions. In the recB mutant, deficient for double-strand break (DSB) repair, fork breakage triggers DSBs in the chromosome terminus during cell division, a reaction that is heritable for several generations. Finally, we recapitulate several observations suggesting that restart from intact inactivated replication forks and restart from recombination intermediates require different sets of enzymatic activities. The finding that 18% of cells suffer replication fork breakage suggests that DNA remains intact at most inactivated forks. Similarly, only 18% of cells need the helicase loader for replication restart, which leads us to speculate that the replicative helicase remains on DNA at intact inactivated replication forks and is reactivated by the replication restart proteins.

    PMID: 29898897 [PubMed - in process]

  • Structural and genomic decoding of human and plant myristoylomes reveals a definitive recognition pattern.

    13 juin, par Castrec B, Dian C, Ciccone S, Ebert CL, Bienvenut WV, Le Caer JP, Steyaert JM, Giglione C, Meinnel T
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    Structural and genomic decoding of human and plant myristoylomes reveals a definitive recognition pattern.

    Nat Chem Biol. 2018 Jun 11;:

    Authors: Castrec B, Dian C, Ciccone S, Ebert CL, Bienvenut WV, Le Caer JP, Steyaert JM, Giglione C, Meinnel T

    Abstract
    An organism's entire protein modification repertoire has yet to be comprehensively mapped. N-myristoylation (MYR) is a crucial eukaryotic N-terminal protein modification. Here we mapped complete Homo sapiens and Arabidopsis thaliana myristoylomes. The crystal structures of human modifier NMT1 complexed with reactive and nonreactive target-mimicking peptide ligands revealed unexpected binding clefts and a modifier recognition pattern. This information allowed integrated mapping of myristoylomes using peptide macroarrays, dedicated prediction algorithms, and in vivo mass spectrometry. Global MYR profiling at the genomic scale identified over a thousand novel, heterogeneous targets in both organisms. Surprisingly, MYR involved a non-negligible set of overlapping targets with N-acetylation, and the sequence signature marks for a third proximal acylation-S-palmitoylation-were genomically imprinted, allowing recognition of sequences exhibiting both acylations. Together, the data extend the N-end rule concept for Gly-starting proteins to subcellular compartmentalization and reveal the main neighbors influencing protein modification profiles and consequent cell fate.

    PMID: 29892081 [PubMed - as supplied by publisher]

  • Ependymal cilia beating induces an actin network to protect centrioles against shear stress.

    13 juin, par Mahuzier A, Shihavuddin A, Fournier C, Lansade P, Faucourt M, Menezes N, Meunier A, Garfa-Traoré M, Carlier MF, Voituriez R, Genovesio A, Spassky N, Delgehyr N
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    Ependymal cilia beating induces an actin network to protect centrioles against shear stress.

    Nat Commun. 2018 Jun 11;9(1):2279

    Authors: Mahuzier A, Shihavuddin A, Fournier C, Lansade P, Faucourt M, Menezes N, Meunier A, Garfa-Traoré M, Carlier MF, Voituriez R, Genovesio A, Spassky N, Delgehyr N

    Abstract
    Multiciliated ependymal cells line all brain cavities. The beating of their motile cilia contributes to the flow of cerebrospinal fluid, which is required for brain homoeostasis and functions. Motile cilia, nucleated from centrioles, persist once formed and withstand the forces produced by the external fluid flow and by their own cilia beating. Here, we show that a dense actin network around the centrioles is induced by cilia beating, as shown by the disorganisation of the actin network upon impairment of cilia motility. Moreover, disruption of the actin network, or specifically of the apical actin network, causes motile cilia and their centrioles to detach from the apical surface of ependymal cell. In conclusion, cilia beating controls the apical actin network around centrioles; the mechanical resistance of this actin network contributes, in turn, to centriole stability.

    PMID: 29891944 [PubMed - in process]

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