The chronostratigraphy of the Haua Fteah cave (Cyrenaica, northeast Libya)

The 1950s excavations by Charles McBurney in the Haua Fteah, a large karstic cave on the coast of northeast Libya, revealed a deep sequence of human occupation. Most subsequent research on North African prehistory refers to his discoveries and interpretations, but the chronology of its archaeological and geological sequences has been based on very early age determinations. This paper reports on the initial results of a comprehensive multi-method dating program undertaken as part of new work at the site, involving radiocarbon dating of charcoal, land snails and marine shell, cryptotephra investigations, optically stimulated luminescence (OSL) dating of sediments, and electron spin resonance (ESR) dating of tooth enamel. The dating samples were collected from the newly exposed and cleaned faces of the upper 7.5 m of the w14.0 m-deep McBurney trench, which contain six of the seven major cultural phases that he identified. Despite problems of sediment transport and reworking, using a Bayesian statistical model the new dating program establishes a robust framework for the five major lithostratigraphic units identified in the stratigraphic succession, and for the major cultural units. The age of two anatomically modern human mandibles found by McBurney in Layer XXXIII near the base of his Levalloiso-Mousterian phase can now be estimated to between 73 and 65 ka (thousands of years ago) at the 95.4% confidence level, within Marine Isotope Stage (MIS) 4. McBurney’s Layer XXV, associated with Upper Palaeolithic Dabban blade industries, has a clear stratigraphic relationship with Campanian Ignimbrite tephra. Microlithic Oranian technologies developed following the climax of the Last Glacial Maximum and the more microlithic Capsian in the Younger Dryas. Neolithic pottery and perhaps domestic livestock were used in the cave from the mid Holocene but there is no certain evidence for plant cultivation until the Graeco-Roman period

A Regulatory Network for Coordinated Flower Maturation

For self-pollinating plants to reproduce, male and female organ development must be coordinated as flowers mature. The Arabidopsis transcription factors AUXIN RESPONSE FACTOR 6 (ARF6) and ARF8 regulate this complex process by promoting petal expansion, stamen filament elongation, anther dehiscence, and gynoecium maturation, thereby ensuring that pollen released from the anthers is deposited on the stigma of a receptive gynoecium. ARF6 and ARF8 induce jasmonate production, which in turn triggers expression of MYB21 and MYB24, encoding R2R3 MYB transcription factors that promote petal and stamen growth. To understand the dynamics of this flower maturation regulatory network, we have characterized morphological, chemical, and global gene expression phenotypes of arf, myb, and jasmonate pathway mutant flowers. We found that MYB21 and MYB24 promoted not only petal and stamen development but also gynoecium growth. As well as regulating reproductive competence, both the ARF and MYB factors promoted nectary development or function and volatile sesquiterpene production, which may attract insect pollinators and/or repel pathogens. Mutants lacking jasmonate synthesis or response had decreased MYB21 expression and stamen and petal growth at the stage when flowers normally open, but had increased MYB21 expression in petals of older flowers, resulting in renewed and persistent petal expansion at later stages. Both auxin response and jasmonate synthesis promoted positive feedbacks that may ensure rapid petal and stamen growth as flowers open. MYB21 also fed back negatively on expression of jasmonate biosynthesis pathway genes to decrease flower jasmonate level, which correlated with termination of growth after flowers have opened. These dynamic feedbacks may promote timely, coordinated, and transient growth of flower organs

Tailoring carbon nanotube surfaces with glyconanorings: new bionanomaterials with specific lectin affinity

3 páginas, 4 figuras, 1 esquema.Remarkably stable, water-soluble glyconanoring-coated SWCNTs were prepared by self organization and photopolymerization of neutral diacetylene-based glycolipids on the nanotube surface; the nanoconstructs are able to engage in specific ligand–lectin interactions in a similar way to glycoconjugates on cell membranes.This work was supported by the DGICyT (grant No. CTQ2006-15515-CO2-01 and CTQ2007-61185), the Junta de Andalucía (grant P06-FQM-01852 and P07-FQM-2774), the CNRS (France) and CSIC (Egide Picasso 09543XA and PICS Program 2008).Peer reviewe

Architecture moléculaire du complexe SAGA de S. cerevisiae

International audienceThe Saccharomyces cerevisiae SAGA complex is a multifunctional coactivator that regulates transcription by RNA polymerase II. The 3D structure of SAGA, revealed by electron microscopy, is formed by five modular domains and shows a high degree of structural conservation to human TFTC, reflecting their related subunit composition. The positions of several SAGA subunits were mapped by immunolabeling and by analysis of mutant complexes. The Taf (TBP-associated factor) subunits, shared with TFIID, occupy a central region in SAGA and form a similar structure in both complexes. The locations of two histone fold-containing core subunits, Spt7 and Ada1, are consistent with their role in providing a SAGA-specific interface with the Tafs. Three components that perform distinct regulatory functions, Spt3, Gcn5, and Tra1, are spatially separated, underscoring the modular nature of the complex. Our data provide insights into the molecular architecture of SAGA and imply a functional organization to the complex

Formation of well-defined soluble aggregates upon fusion to MBP is a generic property of E6 proteins from various human papillomavirus species.

Protein aggregation is a main barrier hindering structural and functional studies of a number of interesting biological targets. The E6 oncoprotein of Human Papillomavirus strain 16 (E6(16)) is difficult to express under a native soluble form in bacteria. Produced as an unfused sequence, it forms inclusion bodies. Fused to the C-terminus of MBP, it is mainly produced in the form of soluble high molecular weight aggregates. Here, we produced as MBP-fusions seven E6 proteins from other HPV strains (5, 11, 18, 33, 45, 52, and 58) belonging to four different species, and we compared their aggregation state to that of MBP-E6(16). Using a fast mutagenesis method, we changed most non-conserved cysteines to the isosteric residue serine to minimize disulfide bridge-mediated aggregation during purification. Static and dynamic light scattering measurements, ultracentrifugation and electron microscopy demonstrated the presence in all MBP-E6 preparations of soluble high-molecular weight aggregates with a well-defined spherical shape. These aggregated particles are relatively monodisperse but their amount and their size vary depending on the conditions of expression and the strain considered. For all strains, minimal aggregate formation occurs when the expression is performed at 15 degrees C. Such observations suggest that the assembly of MBP-E6 aggregates takes place in vivo during protein biosynthesis, rather than occurring during purification. Finally, we show that all MBP-E6 preparations contain two zinc ions per protein monomer, suggesting that E6 domains within the high molecular weight aggregates possess a native-like fold, which enables correct coordination to the metal center

Mapping the initiator binding Taf2 subunit in the structure of hydrated yeast TFIID.

International audienceThe general transcription factor TFIID is a large multisubunit complex required for the transcription of most protein-encoding genes by RNA polymerase II. Taking advantage of a TFIID preparation partially depleted in the initiator-binding Taf2p subunit, we determined the conformational and biochemical variations of the complex by electron tomography and cryo-electron microscopy of single molecules. Image analysis revealed the extent of conformational flexibility of the complex and the selection of the most homogeneous TFIID subpopulation allowed us to determine an improved structural model at 23 Angstroms resolution. This study also identified two subpopulations of Taf2p-containing and Taf2p-depleted TFIID molecules. By comparing these two TFIID species we could infer the position of Taf2p, which was confirmed by immunolabeling using a subunit-specific antibody. Mapping the position of this crucial subunit in the vicinity of Taf1p and of TBP sheds new light on its role in promoter recognition

Mapping histone fold TAFs within yeast TFIID

The transcription factor TFIID is a large multiprotein complex, composed of the TATA box-binding protein (TBP) and 14 TBP-associated factors (TAFs), which plays a key role in the regulation of gene expression by RNA polymerase II. The three-dimensional structure of yeast (y) TFIID, determined at ∼3 nm resolution by electron microscopy and image analysis, resembles a molecular clamp formed by three major lobes connected by thin linking domains. The yTFIID is structurally similar to the human factor although the clamp appears more closed in the yeast complex, probably reflecting the conformational flexibility of the structure. Immunolabelling experiments showed that nine TAFs that contain the histone fold structural motif were located in three distinct substructures of TFIID. The distribution of these TAFs showed that the previously reported pair-wise interactions between histone fold domain (HFD)-containing TAFs are likely to occur in the native yTFIID complex. Most of the HFD-containing TAFs have been found in two distinct lobes, thus revealing an unexpected and novel molecular organization of TFIID

Mapping key functional sites within yeast TFIID

The transcription factor TFIID, composed of the TATA box-binding protein (TBP) and 14 TBP-associated factors (TAFs), plays a key role in the regulation of gene expression by RNA polymerase II. The structure of yeast TFIID, as determined by electron microscopy and digital image analysis, is formed by three lobes, labelled A–C, connected by thin linking domains. Immunomapping revealed that TFIID contains two copies of the WD-40 repeat-containing TAF5 and that TAF5 contributes to the linkers since its C- and N-termini were found in different lobes. This property was confirmed by the finding that a recombinant complex containing TAF5 complexed with six histone fold containing TAFs was able to form a trilobed structure. Moreover, the N-terminal domain of TAF1 was mapped in lobe C, whereas the histone acetyltransferase domain resides in lobe A along with TAF7. TBP was found in the linker domain between lobes A and C in a way that the N-terminal 100 residues of TAF1 are spanned over it. The implications of these data with regard to TFIID function are discussed