Initiation Process (initiation + process)

Distribution by Scientific Domains

Selected Abstracts

Generation and characterization of functional mutants in the translation initiation factor IF1 of Escherichia coli

FEBS JOURNAL, Issue 3 2004
Victor Croitoru
Three protein factors IF1, IF2 and IF3 are involved in the initiation of translation in prokaryotes. No clear function has been assigned to the smallest of these three factors, IF1. Therefore, to investigate the role of this protein in the initiation process in Escherichia coli we have mutated the corresponding gene infA. Because IF1 is essential for cell viability and no mutant selection has so far been described, the infA gene in a plasmid was mutated by site-directed mutagenesis in a strain with a chromosomal infA+ gene, followed by deletion of this infA+ gene. Using this approach, the six arginine residues of IF1 were altered to leucine or aspartate. Another set of plasmid-encoded IF1 mutants with a cold-sensitive phenotype was collected using localized random mutagenesis. All mutants with a mutated infA gene on a plasmid and a deletion of the chromosomal infA copy were viable, except for an R65D alteration. Differences in growth phenotypes of the mutants were observed in both minimal and rich media. Some of the mutated infA genes were successfully recombined into the chromosome thereby replacing the wild-type infA+ allele. Several of these recombinants showed reduced growth rate and a partial cold-sensitive phenotype. This paper presents a collection of IF1 mutants designed for in vivo and in vitro studies on the function of IF1. [source]

Mechanisms for activating bacterial RNA polymerase

Tamaswati Ghosh
Abstract Gene transcription is a fundamental cellular process carried out by RNA polymerase (RNAP) enzymes and is highly regulated through the action of gene regulatory complexes. Important mechanistic insights have been gained from structural studies on multisubunit RNAP from bacteria, yeast and archaea, although the initiation process that involves the conversion of the inactive transcription complex to an active one has yet to be fully understood. RNAPs are unambiguously closely related in structure and function across all kingdoms of life and have conserved mechanisms. In bacteria, sigma (,) factors direct RNAP to specific promoter sites and the RNAP/, holoenzyme can either form a stable closed complex that is incompetent for transcription (as in the case of ,54) or can spontaneously proceed to an open complex that is competent for transcription (as in the case of ,70). The conversion of the RNAP/,54 closed complex to an open complex requires ATP hydrolysis by enhancer-binding proteins, hence providing an ideal model system for studying the initiation process biochemically and structurally. In this review, we present recent structural studies of the two major bacterial RNAP holoenzymes and focus on mechanistic advances in the transcription initiation process via enhancer-binding proteins. [source]

Functional interaction of general transcription initiation factor TFIIE with general chromatin factor SPT16/CDC68

GENES TO CELLS, Issue 4 2000
Seung-Woo Kang
Background Transcriptional initiation of class II genes is one of the major targets for the regulation of gene expression and is carried out by RNA polymerase II and many auxiliary factors, which include general transcription initiation factors (GTFs). TFIIE, one of the GTFs, functions at the later stage of transcription initiation. As recent studies indicated the possibility that TFIIE may have a role in chromatin transcriptional regulation, we isolated TFIIE-interacting factors which have chromatin-related functions. Results Using the yeast two-hybrid screening system, we isolated the C-terminal part of the human homologue of Saccharomyces cerevisiae (y) Spt16p/Cdc68p, a general chromatin factor. The C-terminal part of human SPT16/CDC68 directly interacts with TFIIE, and ySpt16p/Cdc68p also interacts with yTFIIE (Tfa1p/Tfa2p), thus indicating the existence of an evolutionarily conserved interaction between TFIIE and SPT16/CDC68. Functional interaction of yTFIIE and ySpt16p/Cdc68p was examined using a conditional yTFIIE-, mutant strain. Over-expression of ySpt16p/Cdc68p suppressed the phenotype of cold sensitivity of the yTFIIE-,- cs mutant strain, and in vitro binding assays revealed that yTFIIE-,- cs mutant protein showed diminished binding affinity to ySpt16p/Cdc68p. Conclusions These observations indicate that general transcription initiation factor TFIIE functionally interacts with general chromatin factor SPT16/CDC68, a finding which provides new insight into the involvement of TFIIE in chromatin transcription. This may well lead to a breakthrough in relationships between the transcription initiation process and structural changes in chromatin. [source]

Observations of initiation stage of spontaneous vapor explosions for droplet scale

Takeo Takashima
Abstract In this study, the initiation stage of spontaneous vapor explosions generated by single droplets of molten tin submerged in water was investigated using a high- speed video camera operated with a reflected light system. Photographs of the formation process of vapor film, the process of vapor film disturbance, and the initiation process of the vapor explosions for different masses of molten tin and different nozzle diameters were obtained. The results demonstrate that partial thermal interaction between tin and water does not cause a vapor explosion with fragmentation. The vapor film disappears locally during the formation of the vapor film around the hot liquid droplet. Direct contact between the hot molten tin surface and water is thereby generated. However, the local disappearance of the vapor film does not progress and the vapor film is reconstructed. A vapor explosion occurs when the vapor film collapses at the local area of the bottom or edge of the disk-shaped droplet. 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(1): 41,55, 2008; Published online in Wiley InterScience ( DOI 10.1002/htj.20185 [source]

Preparation of gradient copolymers via ATRP using a simultaneous reverse and normal initiation process.


Abstract Spontaneous gradient copolymers were prepared in both bulk and miniemulsion systems via Atom Transfer Radical Polymerization (ATRP) utilizing a Simultaneous Reverse and Normal Initiation (SR & NI) process. Both instantaneous and cumulative compositions were used to characterize the gradient copolymers. The gradient copolymers were obtained with an array of gradient compositions ranging from a subtle to strong variation in monomer distribution along the polymer backbones, depending on the ratio of comonomers initially added to the copolymerization system. The compositions of the gradient copolymer produced in miniemulsion systems were similar to those generated in bulk. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3616,3622, 2005 [source]

Search for highly resolved electron spin resonance spectra of the transient radical in radical polymerization

Mikiharu Kamachi
Abstract The detection of highly resolved spectra in electron spin resonance (ESR) measurements of radical polymerization is presented. Well-resolved ESR spectra of the propagating radical were detected in the radical polymerization of several vinyl monomers with a specially designed cavity and cell. More highly resolved ESR spectra of the propagating radicals of vinyl and diene compounds were observed with aconventional spectrometer without the specially designed cavity and cell. On the basis of the ESR spectra, propagation rate constants and dynamic behavior of propagating radicals are discussed. Moreover, the application of time-resolved ESR spectroscopy to research on the initiation process in radical polymerization is shown. 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 269,285, 2002 [source]

Ring-opening polymerization of ,-caprolactone by a new yttrium complex: Y[2,2,-ethylidene-bis(4,6-di- tert -butylphenoxy)]2(ethylene glycol dimethyl ether)Na(ethylene glycol dimethyl ether)3

Guangming Wu
Abstract The main aims of the work reported here were to synthesize and characterize a new 2,2,-ethylidene-bis(4,6-di- tert -butylphenol) (EDBPH2)-based bimetal yttrium complex, Y(EDBP)2(DME)Na(DME)3 (1c; where DME is ethylene glycol dimethyl ether), which was employed as an efficient initiator for the ring-opening polymerization of ,-caprolactone (,-CL). From single-crystal X-ray diffraction, the solid structure of this new bimetal initiator was well established. Experimental results show that 1c initiates the ring-opening polymerization of ,-CL to afford poly(,-CL) with a narrow molecular weight distribution (Mw/Mn = 1.09,1.36, 65 C). Based on an in situ NMR study, a plausible coordination,insertion mechanism is then proposed. The bimetal complex 1c can be used as an initiator for the ring-opening polymerization of ,-CL with some living characteristics. A study of the mechanism reveals that DME displacement in 1c by ,-CL is involved in the initiation process and the propagation may proceed through three pathways by NaO insertion or YO insertion. Copyright 2009 Society of Chemical Industry [source]