The dnaA initiator protein binds separate domains in the replication origin of Escherichia coli

After binding to its four 9-mer boxes in the 245-base pair Escherichia coli replication origin (oriC), dnaA protein effects the formation of an "open complex" in an adjacent region made up of three 13-mers (Bramhill, D., and Kornberg, A. (1988) Cell 52, 743-755). This open complex formation requires the ATP form of dnaA protein assisted by HU protein (Sekimizu, K., Bramhill, D., and Kornberg, A. (1987) Cell 50, 259-265). We now provide direct evidence that dnaA protein binds the 13-mers, sequences that bear no resemblance to the 9-mer box. The evidence is (i) displacement of dnaA protein from the open complex by oriC or by a synthetic oligonucleotide containing the 13-mers, but not by a mutant of oriC lacking the 13-mers; (ii) filter binding of the synthetic (13-mer) oligonucleotide by dnaA protein; and (iii) requirement for the ATP form of dnaA protein assisted by HU protein for temperature-dependent binding to the 13-mer region. Controlled proteolysis of dnaA protein results in a prompt loss of oriC binding; an NH2-terminal 30-kDa peptide contains the domain that binds ATP and phospholipids known to destabilize the tightly bound ATP.     

Functional Role of Amino-Terminal Serine16 and Serine27 of Gαz in Receptor and Effector Coupling

Abstract: The α subunit of G_z (α_z) harbors two N-terminal serine residues (at positions 16 and 27) that serve as protein kinase C-mediated phosphorylation sites. The cognate residues in the α subunit of G_t1 provide binding surfaces for the β₁ subunit. We used three serine-to-alanine mutants of α_z to investigate the functional importance of the two N-terminal serine residues. Wild-type or mutant α_z was transiently coexpressed with different receptors and adenylyl cyclase isozymes in human embryonic kidney 293 cells, and agonist-dependent regulation of cyclic AMP accumulation was examined in a setting where all endogenous α subunits of G_i were inactivated by pertussis toxin. Replacement of one or both serine residues by alanine did not alter the ability of α_z to interact with δ-opioid, dopamine D₂, or adenosine A₁ receptors. Its capacity to inhibit endogenous and type VI adenylyl cyclases was also unaffected. Functional release of βγ subunits from the mutant α_z subunits was not impaired because they transduced βγ-mediated stimulation of type II adenylyl cyclase. Constitutively active mutants of all four α_z subunits were constructed by the introduction of a Q205L mutation. The activated mutants showed differential abilities to inhibit human choriogonadotropin-mediated cyclic AMP accumulation in luteinizing hormone receptor-transfected cells. Loss of both serine residues, but not either one alone, impaired the receptor-independent inhibition of adenylyl cyclase by the GTPase-deficient mutant. Thus, replacement of the amino-terminal serine residues of α_z has no apparent effect on receptor-mediated responses, but these serine residues may be essential for ensuring transition of α_z into the active conformation.     

Methionine synthesis from 3-methylthioribose in apple tissue

The primary fate of 5-methylthioribose in apple tissue is the formation of methionine. Using dual labeled 5-methylthioribose, it was shown that both the CH₃S- group and the ribose portion of 5-methylthioribose were equally incorporated into methionine. Thus, the pathway involves modification of the ribose portion of 5-methylthioribose into the 2-aminobutyrate portion of methionine. This pathway functions to recycle methionine for continued synthesis of ethylene in fruit tissues. The methionine cycle in relation to ethylene biosynthesis is presented.     

New Class of Ni‐Rich Cathode Materials Li[NixCoyB1−x−y]O2 for Next Lithium Batteries

A new class of layered cathodes, Li[Ni_xCo_yB_1?x?y]O₂ (NCB), is synthesized. The proposed NCB cathodes have a unique microstructure in which elongated primary particles are tightly packed into spherical secondary particles. The cathodes also exhibit a strong crystallographic texture in which the a–b layer planes are aligned along the radial direction, facilitating Li migration. The microstructure, which effectively suppresses the formation of microcracks, improves the cycling stability of the NCB cathodes. The NCB cathode with 1.5 mol% B delivers a discharge capacity of 234 mAh g^?1 at 0.1 C and retains 91.2% of its initial capacity after 100 cycles (compared to values of 229 mAh g^?1 at 0.1 C and 78.8% for pristine Li[Ni_0.9Co_0.1]O₂). This study shows the importance of controlling the microstructure to obtain the required cycling stability, especially for Ni‐rich layered cathodes, where the main cause of capacity fading is related to mechanical strain in their charged state.     

Rhein,a Natural Anthraquinone Derivative,Attenuates the Activation of Pancreatic Stellate Cells and Ameliorates Pancreatic Fibrosis in Mice with Experimental Chronic Pancreatitis

Pancreatic fibrosis, a prominent histopathological feature of chronic pancreatitis (CP) and pancreatic ductal adenocarcinoma, is essentially a dynamic process that leads to irreversible scarring of parenchymal tissues of the pancreas. Though the exact mechanisms of its initiation and development are poorly understood, recent studies suggested that the activation of pancreatic stellate cells (PSCs) plays a critical role in eliciting such active course of fibrogenesis. Anthraquinone compounds possess anti-inflammatory bioactivities whereas its natural derivative rhein has been shown to effectively reduce tissue edema and free-radical production in rat models of inflammatory conditions. Apart from its anti-inflammatory properties, rhein actually exerts strong anti-fibrotic effects in our current in-vivo and in-vitro experiments. In the mouse model of cerulein-induced CP, prolonged administration of rhein at 50 mg/kg/day significantly decreased immunoreactivities of the principal fibrotic activators alpha-smooth muscle actin (α-SMA) and transforming growth factor-beta (TGF-β) on pancreatic sections implicating the activation of PSCs, which is the central tread to fibrogenesis, was attenuated. Consequently, the overwhelmed deposition of extracellular matrix proteins fibronectin 1 (FN1) and type I collagen (COL I-α1) in exocrine parenchyma was found accordingly reduced. In addition, the expression levels of sonic hedgehog (SHH), which plays important roles in molecular modulation of various fibrotic processes, and its immediate effector GLI1 in pancreatic tissues were positively correlated to the degree of cerulein-induced fibrosis. Such up-regulation of SHH signaling was restrained in rhein-treated CP mice. In cultured PSCs, we demonstrated that the expression levels of TGF-β-stimulated fibrogenic markers including α-SMA, FN1 and COL I-α1 as well as SHH were all notably suppressed by the application of rhein at 10 μM. The present study firstly reported that rhein attenuates PSC activation and suppresses SHH/GLI1 signaling in pancreatic fibrosis. With strong anti-fibrotic effects provided, rhein can be a potential remedy for fibrotic and/or PSC-related pathologies in the pancreas.     

Phytochemical Investigation of Annulohypoxylon ilanense,an Endophytic Fungus Derived from Cinnamomum Species

Cultivation of the fungal strain Annulohypoxylon ilanense, an endophytic fungus isolated from the wood of medicinal plant Cinnamomum species, resulted in the isolation of one new furanoid derivative, ilanefuranone ( 1 ), one new pyrrole alkaloid, ilanepyrrolal ( 2 ), and one new biarylpropanoid derivative, ilanenoid ( 3 ), together with 22 known compounds, of which one α‐tetralone analog, (?)‐(4R)‐3,4‐dihydro‐4,6‐dihydroxynaphthalen‐1(2H)‐one ( 4 ) was isolated for the first time from a natural source. The structures were elucidated on the basis of physicochemical evidence, in‐depth NMR spectroscopic analysis, and high‐resolution mass spectrometry, and the antimycobacterial activities were also evaluated.