f(R) theories

Over the past decade, f(R) theories have been extensively studied as one of the simplest modifications to General Relativity. In this article we review various applications of f(R) theories to cosmology and gravity - such as inflation, dark energy, local gravity constraints, cosmological perturbations, and spherically symmetric solutions in weak and strong gravitational backgrounds. We present a number of ways to distinguish those theories from General Relativity observationally and experimentally. We also discuss the extension to other modified gravity theories such as Brans-Dicke theory and Gauss-Bonnet gravity, and address models that can satisfy both cosmological and local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in Relativity, Published version, Comments are welcom

Electron Transfer Function versus Oxygen Delivery: A Comparative Study for Several Hexacoordinated Globins Across the Animal Kingdom

Caenorhabditis elegans globin GLB-26 (expressed from gene T22C1.2) has been studied in comparison with human neuroglobin (Ngb) and cytoglobin (Cygb) for its electron transfer properties. GLB-26 exhibits no reversible binding for O2 and a relatively low CO affinity compared to myoglobin-like globins. These differences arise from its mechanism of gaseous ligand binding since the heme iron of GLB-26 is strongly hexacoordinated in the absence of external ligands; the replacement of this internal ligand, probably the E7 distal histidine, is required before binding of CO or O2 as for Ngb and Cygb. Interestingly the ferrous bis-histidyl GLB-26 and Ngb, another strongly hexacoordinated globin, can transfer an electron to cytochrome c (Cyt-c) at a high bimolecular rate, comparable to those of inter-protein electron transfer in mitochondria. In addition, GLB-26 displays an unexpectedly rapid oxidation of the ferrous His-Fe-His complex without O2 actually binding to the iron atom, since the heme is oxidized by O2 faster than the time for distal histidine dissociation. These efficient mechanisms for electron transfer could indicate a family of hexacoordinated globin which are functionally different from that of pentacoordinated globins

Ovarian cancer molecular pathology.

Peer reviewe

Transcriptional control in the prereplicative phase of T4 development

Control of transcription is crucial for correct gene expression and orderly development. For many years, bacteriophage T4 has provided a simple model system to investigate mechanisms that regulate this process. Development of T4 requires the transcription of early, middle and late RNAs. Because T4 does not encode its own RNA polymerase, it must redirect the polymerase of its host, E. coli, to the correct class of genes at the correct time. T4 accomplishes this through the action of phage-encoded factors. Here I review recent studies investigating the transcription of T4 prereplicative genes, which are expressed as early and middle transcripts. Early RNAs are generated immediately after infection from T4 promoters that contain excellent recognition sequences for host polymerase. Consequently, the early promoters compete extremely well with host promoters for the available polymerase. T4 early promoter activity is further enhanced by the action of the T4 Alt protein, a component of the phage head that is injected into E. coli along with the phage DNA. Alt modifies Arg265 on one of the two α subunits of RNA polymerase. Although work with host promoters predicts that this modification should decrease promoter activity, transcription from some T4 early promoters increases when RNA polymerase is modified by Alt. Transcription of T4 middle genes begins about 1 minute after infection and proceeds by two pathways: 1) extension of early transcripts into downstream middle genes and 2) activation of T4 middle promoters through a process called sigma appropriation. In this activation, the T4 co-activator AsiA binds to Region 4 of σ70, the specificity subunit of RNA polymerase. This binding dramatically remodels this portion of σ70, which then allows the T4 activator MotA to also interact with σ70. In addition, AsiA restructuring of σ70 prevents Region 4 from forming its normal contacts with the -35 region of promoter DNA, which in turn allows MotA to interact with its DNA binding site, a MotA box, centered at the -30 region of middle promoter DNA. T4 sigma appropriation reveals how a specific domain within RNA polymerase can be remolded and then exploited to alter promoter specificity

The Confrontation between General Relativity and Experiment

The status of experimental tests of general relativity and of theoretical frameworks for analysing them is reviewed. Einstein's equivalence principle (EEP) is well supported by experiments such as the Eotvos experiment, tests of special relativity, and the gravitational redshift experiment. Future tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, and the Nordtvedt effect in lunar motion. Gravitational-wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and other binary pulsar systems have yielded other tests, especially of strong-field effects. When direct observation of gravitational radiation from astrophysical sources begins, new tests of general relativity will be possible.Comment: 89 pages, 8 figures; an update of the Living Review article originally published in 2001; final published version incorporating referees' suggestion

Molecular Characterization of Vibrio Cholerae �relA �spoT Double Mutants

In Escherichia coli cellular levels of pppGpp and ppGpp, collectively called (p)ppGpp, are maintained by the products of two genes, relA and spoT. Like E. coli, Vibrio cholerae also possesses relA and spoT genes. Here we show that similar to E. coli, V. cholerae �relA cells can accumulate (p)ppGpp upon carbon starvation but not under amino acid starved condition. Although like in E. coli, the spoT gene function was found to be essential in V. cholerae relA+ background, but unlike E. coli, several V. cholerae �relA �spoT mutants constructed in this study accumulated (p)ppGpp under glucose starvation. The results suggest a cryptic source of (p)ppGpp synthesis in V. cholerae, which is induced upon glucose starvation. Again, unlike E. coli �relA �spoT mutant (ppGpp0 strain), the V. cholerae �relA �spoT mutants showed certain unusual phenotypes, which are (a) resistance towards 3-amino-1,2,4-triazole (AT); (b) growth in nutrient poor M9 minimal medium; (c) ability to stringently regulate cellular rRNA accumulation under glucose starvation and (d) initial growth defect in nutrient rich medium. Since these phenotypes of �relA �spoT mutants could be reverted back to �relA phenotypes by providing SpoT in trans, it appears that the spoT gene function is crucial in V. cholerae