The Central Asian Orogenic Belt (CAOB) is a natural laboratory for the study of accretionary tectonics and crustal growth owing to its massive generation of juvenile crust in the Paleozoic. There is a debate, however, on the mechanism of this growth. In the Baogutu area of the western Junggar region, northern Xinjiang (west China), diorite-granodiorite porphyry plutons and dikes are widely associated with Cu-Au mineralization. In this study, we present new results of zircon U-Pb geochronology, major and trace elements, and Sr-Nd-Pb-Hf isotope analyses for two diorite-granodiorite porphyry plutons and two dikes from this area. LA-ICPMS zircon U-Pb analyses of four plutonic and dike samples yield Late Carboniferous ages of 315 -310 Ma. The Baogutu diorite-granodiorite porphyries exhibit low-Fe and calc-alkaline compositions. They are also geochemically characterized by high Sr (346-841 ppm) contents, low Y (9.18-16.5 ppm) and Yb (0.95-1.60 ppm) contents, and relatively high Sr/Y (31-67) ratios, which are similar to those of typical adakites. In addition, some samples have relatively high MgO (2.35-8.32 wt.%) and Mg # (48-75) values, and Cr (22.7-291 ppm) and Ni (32.0-132 ppm) contents, which are similar to those of high-Mg andesites. All rock samples exhibit mid-oceanic ridge basalt (MORB)-like Nd-Sr-Pb-Hf isotope features: high ε Nd (t) (+5.8-+8.3) and ε Hf (t) (+13.1-+15.7) values, and relatively low ( 87 Sr/ 86 Sr) i (0.7033 to 0.7054) and ( 206 Pb/ 204 Pb) i (17.842-18.055). The Baogutu adakitic rocks also contain reversely zoned clinopyroxene phenocrysts, which have low MgO cores and relatively high MgO rims. Geochemical modeling indicates that the Baogutu adakitic rocks could have been derived by mixing ~95% altered oceanic crust-derived melts with ~5%sediment-derived melts. Taking into account the regional geology, I-and A-type granitoids and Cu-Au mineralization, and the presence of Carboniferous ophiolite mé langes in northern Xinjiang, we suggest that the Baogutu adakitic rocks were most probably generated by partial melting of a slab edge close to a subducting spreading ridge 3 in the Late Carboniferous. Ridge subduction and the resultant slab window probably caused strong extension in the overlying lithosphere, extensive melting of subducting oceanic crust, mantle and juvenile lower crust, and interaction between slab-derived melts and the mantle. Thus, events associated with ridge subduction are likely to have played an important role in crustal growth in the CAOB in addition to previously recognized accretion of subduction and arc complexes and post-collisional crustal melting.

Voluminous Late Paleozoic igneous rocks and associated Cu-Au-Mo deposits occur in the northwestern Tianshan district, Xinjiang, west China. However, the tectonic setting and petrogenesis of these rocks remain controversial. This paper reports zircon U-Pb and Hf isotopic data, major and trace elements, and Sr-Nd-Pb isotopic data for the intrusive rocks and minor dacites in the Lamasu-Dabate area of northwestern Tianshan adjacent to the Cu-Au-Mo deposits. LA-ICPMS U-Pb zircon analyses suggest that the Lamasu porphyries were formed at 366 ± 3 Ma and contain 907-738 Ma inherited zircons, the Dabate dacites were formed at 316 ± 4 Ma, and granite porphyries were formed at 289 ± 3 Ma with ~ 319 Ma inherited zircons. The Lamasu porphyries consist of plagioclase granite and granodiorite, and are geochemically similar to adakites, e.g., having high Al 2 O 3 (14.54-19.75 wt.%) and Sr (308-641 ppm) and low Y (7.84-16.9 ppm) contents, with fractionated rare earth element (REE) patterns and slightly positive Sr anomalies. However, they have variable initial ratios of 87 Sr/ 86 Sr (0.7072-0.7076) and 206 Pb/ 204 Pb (18.139-18.450), and variable ε Nd (t) (-5.6 to-0.8) and positive ε Hf (t) (+1.4 to +10.6) values. They also have variable Mg # (100×Mg 2+ /(Mg 2+ +Fe 2+)) (41-73) and low Th (3.13-8.09) and Th/Ce (0.14-0.28) values. We suggest that the Lamasu adakitic magmas were generated through partial melting of southward subducted Junggar oceanic crust, with subsequent melt-mantle interaction and assimilation of basement rocks. The Dabate dacites show typical arc-like geochemical characteristics (e.g., enrichment of large ion lithophile elements (LILE) and strong negative anomalies of Ta, Nb, P and Ti), with variable ε Nd (t) (+0.1 to +3.3). They were probably generated by melting of juvenile basaltic lower crust as a result of magma underplating. The Dabate granite porphyries are geochemically similar to A 2-type granites, e.g., high SiO 2 (75.6-77.6 wt.%) and alkalis (Na 2 O+K 2 O = 8.27-8.70 wt.%), low CaO (0.28-0.34 wt.%) and Mg # (2-10), and obvious negative Eu, Ba and Sr anomalies. They have variable values of ε Nd (t) (-1.7 to 0) and 206 Pb/ 204 Pb i (18.567-18.721) and zircon ε Hf (t) (+0.5 to +11.1). The Dabate A-type granite porphyries contain Late Carboniferous residual zircon cores, suggesting that their source rock possibly contained Carboniferous arc igneous rocks. Taking into account all available data from Late Paleozoic magmatic rocks and Cu-Mo-Au mineralization in the northern Tianshan district, we suggest that the Dabate-Lamasu area was a continental arc during the Late Devonian-Carboniferous but had entered a post-collisional stage by the Early-Permian (~ 290 Ma).

The regulatory network and biological functions of the fungal secondary metabolite oosporein have remained obscure. Beauveria bassiana has evolved the ability to parasitize insects and outcompete microbial challengers for assimilation of host nutrients. A novel zinc finger transcription factor, BbSmr1 (B. bassiana secondary metabolite regulator 1), was identified in a screen for oosporein overproduction. Deletion of Bbsmr1 resulted in up-regulation of the oosporein biosynthetic gene cluster (OpS genes) and constitutive oosporein production. Oosporein production was abolished in double mutants of Bbsmr1 and a second transcription factor, OpS3, within the oosporein gene cluster (ΔBbsmr1ΔOpS3), indicating that BbSmr1 acts as a negative regulator of OpS3 expression. Real-time quantitative PCR and a GFP promoter fusion construct of OpS1, the oosporein polyketide synthase, indicated that OpS1 is expressed mainly in insect cadavers at 24-48 h after death. Bacterial colony analysis in B. bassiana-infected insect hosts revealed increasing counts until host death, with a dramatic decrease (∼90%) after death that correlated with oosporein production. In vitro studies verified the inhibitory activity of oosporein against bacteria derived from insect cadavers. These results suggest that oosporein acts as an antimicrobial compound to limit microbial competition on B. bassiana-killed hosts, allowing the fungus to maximally use host nutrients to grow and sporulate on infected cadavers.Beauveria bassiana | oosporein | biological role | transcription factor | fungal-bacterial competition

There is considerable controversy over the nature of geophysically recognized low-velocity–high-conductivity zones (LV–HCZs) within the Tibetan crust, and their role in models for the development of the Tibetan Plateau. Here we report petrological and geochemical data on magmas erupted 4.7–0.3 Myr ago in central and northern Tibet, demonstrating that they were generated by partial melting of crustal rocks at temperatures of 700–1,050 °C and pressures of 0.5–1.5 GPa. Thus Pliocene-Quaternary melting of crustal rocks occurred at depths of 15–50 km in areas where the LV–HCZs have been recognized. This provides new petrological evidence that the LV–HCZs are sources of partial melt. It is inferred that crustal melting played a key role in triggering crustal weakening and outward crustal flow in the expansion of the Tibetan Plateau.

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alpha-Lytic protease is encoded with a large (166 amino acid) N-terminal pro region that is required transiently both in vivo and in vitro for the correct folding of the protease domain [Silen, J. L. , and Agard, D. A. (1989) Nature 341, 462-464; Baker, D., et al. (1992) Nature 356, 263-265]. The pro region also acts as a potent inhibitor of the mature enzyme [Baker, D., et al. (1992) Proteins: Struct.,Funct., Genet. 12, 339-344]. This inhibition is mediated through direct steric occlusion of the active site by the C-terminal residues of the pro region [Sohl, J. L., et al. (1997) Biochemistry 36, 3894-3904]. Through mutagenesis and structure-function analyses we have begun to investigate the mechanism by which the pro region acts as a single turnover catalyst to facilitate folding of the mature protease. Of central interest has been mapping the interface between the pro region and the protease and identifying interactions critical for stabilizing the rate-limiting folding transition state. Progressive C-terminal deletions of the pro region were found to have drastic effects on the rate at which the pro region folds the protease but surprisingly little effect on inhibition of protease activity. The observed kinetic data strongly support a model in which the detailed interactions between the pro region C-terminus and the protease are remarkably similar to those of known substrate/inhibitor complexes. Further, mutation of two protease residues near the active site have significant effects on stabilization of the folding transition state (kcat) or in binding to the folding intermediate (KM). Our results suggest a model for the alpha-lytic protease pro region-mediated folding reaction that may be generally applicable to other pro region-dependent folding reactions.

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