Search Results - (Author, Cooperation:M. Buck)

2018-06-01

American Chemical Society (ACS)

Chemistry and Pharmacology

2018-09-29

Nature Publishing Group (NPG)

2041-1723

Biology

Chemistry and Pharmacology

Natural Sciences in General

Physics

2018-11-10

The American Society for Biochemistry and Molecular Biology (ASBMB)

0021-9258

1083-351X

Biology

Chemistry and Pharmacology

2015-08-22

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Crystallography, X-Ray ; Enzyme Stability ; *Evolution, Molecular ; *Gene Expression Regulation ; Holoenzymes/chemistry ; Protein Conformation ; Protein Structure, Tertiary ; RNA Polymerase Sigma 54/*chemistry/genetics ; *Transcription, Genetic

0040-4020

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Chemistry and Pharmacology

Electronic Resource

2018-01-26

American Society of Hematology (ASH)

0006-4971

1528-0020

Biology

Medicine

Phagocytes, Granulocytes, and Myelopoiesis

2018-03-17

American Physical Society (APS)

1098-4402

Physics

Radio Frequency Calculations and Technology

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A chemical vapor deposition method is described for fabricating force microscope cantilevers with single-crystal diamond tips. The (approximately-equal-to)1-μm-diam diamond tips have corner radii of 30 nm, and have been used to study diamond–diamond friction on well-characterized surfaces in UHV. The tip size and orientation can be determined by electron microscopy without altering the surface atomic structure.

Electronic Resource

1525-1438

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

A 54-year-old woman with inoperable metastatic small cell carcinoma (SCC) of the endometrium was treated with cisplatin and etoposide chemotherapy on the basis of the histologic similarity to pulmonary SCC. The response to treatment was monitored using serum neuron specific enolase (NSE) levels. A complete remission was obtained with resolution of symptoms and disappearance of the mass. The patient is alive and well 4½ years later. Considering the aggressive behavior and short survival usually associated with this tumor and the presence of such advanced disease, a complete response to chemotherapy was unexpected. It would appear that chemotherapy should always be considered in the management of metastatic endometrial SCC, even in the presence of large-volume disease.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

In a hot-filament reactor diamond films were deposited on various substrates without pretreatment. A nickel wire placed at a short distance above the substrate yields an increase of the nucleation density by five orders of magnitude. Closed diamond films were obtained for different substrate materials. The deposits were characterized by scanning electron microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. The presence of Ni in the diamond films indicates that Ni containing species are transported through the gas phase during the reaction to the substrate surface thus forming nucleation centers. Replacing the Ni wire by a diamond membrane nucleation enhancement is reduced by about three orders of magnitude. The pronounced distance dependence observed suggests that volatile unstable species are produced which form nucleation centers upon impact on the substrate surface. © 1995 American Institute of Physics.

Electronic Resource

1365-2958

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Medicine

Transcriptional activator proteins that act upon the σ54-containing form of the bacterial RNA polymerase belong to the extensive AAA+ superfamily of ATPases, members of which are found in all three kingdoms of life and function in diverse cellular processes, often via chaperone-like activities. Formation and collapse of the transition state of ATP for hydrolysis appears to engender the interaction of the activator proteins with σ54 and leads to the protein structural transitions needed for RNA polymerase to isomerize and engage with the DNA template strand. The common oligomeric structures of AAA+ proteins and the crea-tion of the active site for ATP hydrolysis between protomers suggest that the critical changes in protomer structure required for productive interactions with σ54-holoenzyme occur as a consequence of sensing the state of the γ-phosphate of ATP. Depending upon the form of nucleotide bound, different functional states of the activator are created that have distinct substrate and chaperone-like binding activ-ities. In particular, interprotomer ATP interactions rely upon the use of an arginine finger, a situation reminiscent of GTPase-activating proteins.

Electronic Resource

1365-2958

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Medicine

Enhancer-dependent transcription in bacteria requires the alternative transcription factor σN (σ54), which forms an RNA polymerase holoenzyme that binds promoters as a transcriptionally inactive complex. We have examined the structure of σN by circular dichroism (CD) analysis. The σN protein and its domains are well structured in the absence of the core RNA polymerase subunits or promoter DNA. Denaturation of σN by temperature as followed by changes in CD shows a concomitant loss of secondary and tertiary structures with a melting temperature of 36°C. The secondary structure displays a two-state melting curve with a second Tm of 85°C. The amino-terminal Region I activation domain together with the acidic Region II does not contribute to the two-state melting. In marked contrast, the integrity of the C-terminal DNA-binding domain is required for the two-state melting. Measurements of pKb also demonstrated that a C-terminal part of σN, but not regions I or I + II, is required for the structural integrity of σN at high pH. Measurements of pKa suggested that α-helical structures are important in σN for the establishment of tertiary structural elements. The tertiary structure near ultraviolet CD signals of σN do not require regions I or I + II but were strongly diminished by C-terminal truncation of σN. Promoter DNA binding resulted in aconformational change in σN, permitting the determination of a binding constant. A typical B-DNA conformation was adopted by the promoter DNA. Implications for the modular domain organization of σN, the function of C-terminal sequences, and domain communication and its role in activation of transcription are discussed.

Electronic Resource

1365-2958

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Medicine

The transcription factor sigma-54 (σ54) is a sequence-specific DNA-binding protein that directs RNA polymer a se to a particular class of promoter. The interaction of σ54 with promoter DNA has been analysed by protein-DNA crosslinking and enzymatic and chemical proteolysis. Direct physical evidence for a DNA-contacting surface within the carboxy-terminal one-third of the protein has been obtained. This region of σ54 is likely to be close to the surface of the protein, and contacts DNA when either o54 or the σ54-holoenzyme bind specifically to promoter DNA. The amino-terminal region of σ54 appears to be highly susceptible to proteolysis, and its integrity influences the accessibility towards proteolysis of a second region of σ54, which includes the DNA-contacting surface. Thus the amino-terminal region of σ54 may have a role in influencing its DNA-binding properties, the major determinants of which appear to reside in the carboxy-terminal one-third of the protein.

Electronic Resource

1365-2958

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Medicine

Using directed mutagenesis, amino acid substitutions have been made in the α- and β-subunits of the Klebsiella pneumoniae nitrogenase component 1 at positions normally occupied by conserves cysteine or tyrosine residues. Nif', Nif and intermediate pheno-types have been obtained. To extend our earlier biochemical characterization (Kent et al, 1989) the electrophoretic mobiliy of component 1 of the mutant and wild-type nitrogenases has been analysed by non-denaturing gel electrophoresis. The major and minor forms of component 1 separated by this methodology have been probed for by using both polyclonal and monoclonal antibodies. All Nif mutants exhibited a distribution of electrophoretic forms of component 1 comparable to the wild type, and the abundance of the major from found in purified nitrogennase correlated approximately with the specific activity of the extract. In contrast, after electrophoresis, component 1 from Nif mutants exhibited either a major low-mobility from or a fast-moving from. Analysis of co-factor (FeMoco) allowed us to conclude that changing cysteine 275 to alanine in the α-submit produces component 1 defective in its interaction with FeMoco. Substitution of other con-served cysteine residues by alanine appears to prevent early steps in nitrogebnase assembly or to promote degradation. Two single mutations (cysteine89 to alanine in the β-subunit) which are tightly Nif can be combined to produce a weakly active nitrogenase, indicating regions involved in the interaction between subunits.

Electronic Resource

1365-2958

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Medicine

Transcriptional activation of nitrogen fixation genes by Nrt A in Klebsiella pneumoniae requires an upstream Nif A binding site. We now report that the introduction of haif turns of the DNA helix into the DNA separating the upstream NifA binding site from the downstream promoter element of the nifH promoter decreases Nif A-mediated activation to a greater extent than does the introduction of full helical turns. Reducing the spacing between the upstream and downstream elements of the nifH promoter also results in a promoter down phenotype. Introduction of a tight protein-binding site, the lac operator, between the upstream and downstream promoter elements did not render activation of the nifH promoter sensitive to occupancy of this site by the lac repressor. These findings indicate that NifA-mediated activation of transcription requires that NifA is bound upstream, and to the correct face of the DNA helix, in order to interact with downstream transcription factors. This implies that the interaction is brought about by the formation of a DNA loop between upstream and downstream promoter elements rather than by NifA sliding downstream.The authors wish to thank Ray Dixon, Martin Drummond, Mike Merrick, and John Postgate for their constructive comments on the manuscript, and Beryl Scutt for typing the manuscript.

Electronic Resource

1365-2958

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Medicine

The influence of the Klebsiella pneumoniae nifL gene product upon the interaction of the transcriptional activator protein NifA with the nifH promoter has been examined using in vivo dimethylsulphate ‘footprinting’. Binding of NifA to the upstream activator sequence (UAS) of the nifH promoter in the presence of the NifL protein was observed under nitrogen-limiting growth conditions. Growth in the presence of NH+4 or addition of NH+4 to nitrogen-limited cells diminished the interaction of NifA with the UAS when NifL was present. Repression of nif transcription by NifL may therefore involve an interaction between NifL and NifA which reduces the affinity of NifA for the UAS.

Electronic Resource

0025-8385

Linguistics and Literary Studies

REVIEWS

0025-8385

Linguistics and Literary Studies

REVIEWS

0167-4781

Modifying enzyme ; Recognition site ; Sequence specificity ; tRNA modification

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Medicine

Physics

Electronic Resource

0378-1119

M 13 heteroduplex ; Recombinant DNA ; nitrogen control ; nitrogen fixation ; sodium bisulphite ; transcriptional activation

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Electronic Resource