Protein-protein interactions play crucial roles in the execution of various biological functions. Accordingly, their comprehensive description would contribute considerably to the functional interpretation of fully sequenced genomes, which are flooded with novel genes of unpredictable functions. We previously developed a system to examine two-hybrid interactions in all possible combinations between the Ϸ6,000 proteins of the budding yeast Saccharomyces cerevisiae. Here we have completed the comprehensive analysis using this system to identify 4,549 two-hybrid interactions among 3,278 proteins. Unexpectedly, these data do not largely overlap with those obtained by the other project [Uetz, P., et al.
Protein-protein interactions play pivotal roles in various aspects of the structural and functional organization of the cell, and their complete description is indispensable to thorough understanding of the cell. As an approach toward this goal, here we report a comprehensive system to examine two-hybrid interactions in all of the possible combinations between proteins of Saccharomyces cerevisiae. We cloned all of the yeast ORFs individually as a DNA-binding domain fusion (''bait'') in a MATa strain and as an activation domain fusion (''prey'') in a MAT␣ strain, and subsequently divided them into pools, each containing 96 clones. These bait and prey clone pools were systematically mated with each other, and the transformants were subjected to strict selection for the activation of three reporter genes followed by sequence tagging. Our initial examination of Ϸ4 ؋ 10 6 different combinations, constituting Ϸ10% of the total to be tested, has revealed 183 independent two-hybrid interactions, more than half of which are entirely novel. Notably, the obtained binary data allow us to extract more complex interaction networks, including the one that may explain a currently unsolved mechanism for the connection between distinct steps of vesicular transport. The approach described here thus will provide many leads for integration of various cellular functions and serve as a major driving force in the completion of the protein-protein interaction map.
Many biochemical, physiological and behavioural processes in organisms ranging from microorganisms to vertebrates exhibit circadian rhythms. In Drosophila, the gene period (per) is required for the circadian rhythms of locomotor activity and eclosion behaviour. Oscillation in the levels of per mRNA and Period (dPer) protein in the fly brain is thought to be responsible for the rhythmicity. However, no per homologues in animals other than insects have been identified. Here we identify the human and mouse genes (hPER and mPer, respectively) encoding PAS-domain (PAS, a dimerization domain present in Per, Amt and Sim)-containing polypeptides that are highly homologous to dPer. Besides this structural resemblance, mPer shows autonomous circadian oscillation in its expression in the suprachiasmaticnucleus, which is the primary circadian pacemaker in the mammalian brain. Clock, a mammalian clock gene encoding a PAS-containing polypeptide, has now been cloned: it is likely that the Per homologues dimerize with other molecule(s) such as Clock through PAS-PAS interaction in the circadian clock system.
The crystal structures of 1-butyl-3-methylimidazolium chloride [bmim]Cl and 1-butyl-3-methylimidazolium bromide [bmim]Br show that two rotational isomers, the TT form and the GT form, of the [bmim]+ cation exist in the crystalline state. A vibrational analysis based on a DFT calculation indicates that two characterstic Raman bands of crystalline [bmim]Cl and three of crystalline [bmim]Br can be used as marker bands of the rotational isomerism around the C7–C8 bond of the n-butyl group. The Raman spectra of liquid [bmim]BF4, in which both sets of marker bands are simultaneously observed, then prove that at least two rotational isomers of the [bmim]+ cation coexist in the ionic liquid state.
A prototype ionic-liquid [bmim]Cl shows crystal polymorphism, having two crystal forms, Crystal (1) and Crystal (2), characterized by distinct X-ray powder patterns and Raman spectra. Two sets of characteristic Raman bands of Crystals (1) and (2), which are mutually exclusive with each other, do coexist in the spectrum of liquid [bmim]Cl. It seems that two distinct structures of the [bmim]+ ion, one corresponding to that in Crystal (1) and the other to that in Crystal (2), exist simultaneously in the ionic liquid state.
Mixtures of ionic liquid (IL, 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4]) and water with varying concentrations were studied by attenuated total reflection infrared absorption and Raman spectroscopy. Changes in the peak intensities and peak positions of CHx (x = 1, 2, 3) vibration modes of the cation of the IL and OH vibration modes of the water molecules were investigated. Peaks from normal-mode stretch vibrations of CH bonds belonging to the imidazolium ring of the cation did not change their positions, while those from the terminal methyl group of the butyl chain blueshifted by approximately 10 cm-1 with the addition of water. On the other hand, change in the spectral shape in the OH stretch vibration region shows hydrogen-bonding network of water molecules breaking down rapidly as the IL is added. Trends in the change of the peak positions and the peak intensities suggested qualitative change of the intermolecular structure in the [BMIM][BF4] + H2O mixture at 32 +/- 2 and 45 +/- 2 mol/L of water concentration.
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