PCAF regulates the stability of the transcriptional regulator and cyclin-dependent kinase inhibitor p27Kip1

P27(Kip1) (p27) is a member of the Cip/Kip family of cyclin-dependent kinase inhibitors. Recently, a new function of p27 as transcriptional regulator has been reported. It has been shown that p27 regulates the expression of target genes mostly involved in splicing, cell cycle, respiration and translation. We report here that p27 directly binds to the transcriptional coactivator PCAF by a region including amino acids 91-120. PCAF associates with p27 through its catalytic domain and acetylates p27 at lysine 100. Our data showed that overexpression of PCAF induces the degradation of p27 whereas in contrast, the knockdown of PCAF stabilizes the protein. A p27 mutant in which K100 was substituted by arginine (p27-K100R) cannot be acetylated by PCAF and has a half-life much higher than that of p27WT. Moreover, p27-K100R remains stable along cell-cycle progression. Ubiquitylation assays and the use of proteasome inhibitors indicate that PCAF induces p27 degradation via proteasome. We also observed that knockdown of skp2 did not affect the PCAF induced degradation of p27. In conclusion, our data suggest that the p27 acetylation by PCAF regulates its stability.

Finite-size scaling investigation of the liquid-liquid critical point in ST2 water and its stability with respect to crystallization.

The liquid-liquid critical point scenario of water hypothesizes the existence of two metastable liq- uid phases low-density liquid (LDL) and high-density liquid (HDL) deep within the supercooled region. The hypothesis originates from computer simulations of the ST2 water model, but the stabil- ity of the LDL phase with respect to the crystal is still being debated. We simulate supercooled ST2 water at constant pressure, constant temperature, and constant number of molecules N for N ≤ 729 and times up to 1 μs. We observe clear differences between the two liquids, both structural and dynamical. Using several methods, including finite-size scaling, we confirm the presence of a liquid-liquid phase transition ending in a critical point. We find that the LDL is stable with respect to the crystal in 98% of our runs (we perform 372 runs for LDL or LDL-like states), and in 100% of our runs for the two largest system sizes (N = 512 and 729, for which we perform 136 runs for LDL or LDL-like states). In all these runs, tiny crystallites grow and then melt within 1 μs. Only for N ≤ 343 we observe six events (over 236 runs for LDL or LDL-like states) of spontaneous crystal- lization after crystallites reach an estimated critical size of about 70 ± 10 molecules.

Urban population density functions : the case of the Barcelona region

L'anàlisi de la densitat urbana és utilitzada per examinar la distribució espacial de la població dins de les àrees urbanes, i és força útil per planificar els serveis públics. En aquest article, s'estudien setze formes funcionals clàssiques de la relació existent entre la densitat i la distancia en la regió metropolitana de Barcelona i els seus onze subcentres.

Stability and asymptotic analysis of a fluid-particle interaction model

We are interested in coupled microscopic/macroscopic models describing the evolution of particles dispersed in a fluid. The system consists in a Vlasov-Fokker-Planck equation to describe the microscopic motion of the particles coupled to the Euler equations for a compressible fluid. We investigate dissipative quantities, equilibria and their stability properties and the role of external forces. We also study some asymptotic problems, their equilibria and stability and the derivation of macroscopic two-phase models.

On dictatorship, economic development and stability

This paper aims to account for varying economic performances and political stability under dictatorship. We argue that economic welfare and social order are the contemporary relevant factors of political regimes' stability. Societies with low natural level of social order tend to tolerate predatory behavior from dictators in exchange of a provision of civil peace. The fear of anarchy may explain why populations are locked in the worst dictatorships. In contrast, in societies enjoying a relative natural civil peace, dictatorship is less likely to be predatory because low economic welfare may destabilize it.

Paths to stability for matching markets with couples

We study two-sided matching markets with couples and show that for a natural preference domain for couples, the domain of weakly responsive preferences, stable outcomes can always be reached by means of decentralized decision making. Starting from an arbitrary matching, we construct a path of matchings obtained from `satisfying' blocking coalitions that yields a stable matching. Hence, we establish a generalization of Roth and Vande Vate's (1990) result on path convergence to stability for decentralized singles markets. Furthermore, we show that when stable matchings exist, but preferences are not weakly responsive, for some initial matchings there may not exist any path obtained from `satisfying' blocking coalitions that yields a stable matching.

Candidate stability and voting correspondences

We study the incentives of candidates to enter or to exit elections in order to strategically affect the outcome of a voting correspondence. We extend the results of Dutta, Jackson and Le Breton (2000), who only considered single-valued voting procedures by admitting that the outcomes of voting may consist of sets of candidates. We show that, if candidates form their preferences over sets according to Expected Utility Theory and Bayesian updating, every unanimous and non dictatorial voting correspondence violates candidate stability. When candidates are restricted to use even chance prior distributions, only dictatorial or bidictatorial rules are unanimous and candidate stable. We also analyze the implications of using other extension criteria to define candidate stability that open the door to positive results.

On the stability of cooperation structures

Qin [J. Eco. Th., 1996] recently showed that in a game of endogenous formation of cooperation structure, if the underlying TU-game is superadditive, then the full cooperation structure is stable. In this note, we characterize the class of games that ensure the stability of the full cooperation structure, and show that this class is much larger than that of superadditive TU-games.

Employment descentralisation: polycentric compaction or sprawl? The case of the Barcelona Metropolitan Region 1986-1996

The Barcelona Metropolitan Region (BMR) has been repeatedly characterised as a polycentric-type urban system. The aim of this study is to corroborate this affirmation by making use of a methodology that enables the identifying of employment subcentres and valuing of the degree of polycentrism of the BMR in 1986 and 1996. The results obtained in the two years confirm the existence and extension of the polycentrism.

Reduction, Linearization and stability of relative equilibria for mechanical systems on riemannian manifolds

Consider a Riemannian manifold equipped with an infinitesimal isometry. For this setup, a unified treatment is provided, solely in the language of Riemannian geometry, of techniques in reduction, linearization, and stability of relative equilibria. In particular, for mechanical control systems, an explicit characterization is given for the manner in which reduction by an infinitesimal isometry, and linearization along a controlled trajectory "commute." As part of the development, relationships are derived between the Jacobi equation of geodesic variation and concepts from reduction theory, such as the curvature of the mechanical connection and the effective potential. As an application of our techniques, fiber and base stability of relative equilibria are studied. The paper also serves as a tutorial of Riemannian geometric methods applicable in the intersection of mechanics and control theory.

Stability and manipulation in representative democracies

This paper is devoted to the analysis of all constitutions equipped with electoral systems involving two step procedures. First, one candidate is elected in every jurisdiction by the electors in that jurisdiction, according to some aggregation procedure. Second, another aggregation procedure collects the names of the jurisdictional winners in order to designate the final winner. It appears that whenever individuals are allowed to change jurisdiction when casting their ballot, they are able to manipulate the result of the election except in very few cases. When imposing a paretian condition on every jurisdictions voting rule, it is shown that, in the case of any finite number of candidates, any two steps voting rule that is not manipulable by movement of the electors necessarily gives to every voter the power of overruling the unanimity on its own. A characterization of the set of these rules is next provided in the case of two candidates.

Stability of periodic solutions obtained via the averaging method for nonsmooth Lipschitz system

"Vegeu el resum a l'inici del document del fitxer adjunt."

On the stability of periodic orbits in Rn

We consider an autonomous differential system in Rn with a periodic orbit and we give a new method for computing the characteristic multipliers associated to it. Our method works when the periodic orbit is given by the transversal intersection of n ¡ 1 codimension one hypersurfaces and is an alternative to the use of the first order variational equations. We apply it to study the stability of the periodic orbits in several examples, including a periodic solution found by Steklov studying the rigid body dynamics.

Propietats d'absorció bifotònica del tetrafenilporficè i el seu complex de palladi: potencials sensibilitzadors per a Teràpia Fotodinàmica bifotònica.

Estudi elaborat a partir d’una estada a la Universitat de Aarhus, Dinamarca, durant juliol 2006. En el present treball s’investiguen, per primer cop, les propietats de absorció bifotòniques del fotosensibilitzador 2,7,12,17-tetrafenilporficè (TPPo) i del seu complex de pal•ladi (II) (PdTPPo). Ambos compostos han rebut molta atenció com a possibles otosensibilitzadors per a Teràpia Fotodinàmica (TFD). S’utilitza la detecció de la fosforescència de l’oxigen singlet, centrada a 1270 nm i produïda per l’absorció de dos fotons, per quantificar la magnitud de la secció d’absorció bifotònica, "delta", dels porficèns estudiats. Els experiments se han dut a terme en el marge espectral 750-850 nm i a l’infraroig proper a 1100nm. Aquestes longituds d’ona corresponen a les zones d’absorció bifotònica en les bandes de Soret i Q. Les propietats bifotòniques obtingudes es comparen i contrasten amb les dades conegudes de la tetrafenilporfirina (TPP), isòmer estructural del tetrafenilporficè però amb més gran simetria, i es troba que en la banda de Soret (que coincideix amb la regió de la pell més transparent) els valors de delta per el TPPo i PdTPPo son aproximadament 2000 GM en el màxim, pràcticament cent vegades més grans que per la TPP. A més a més, aquestos valors son dos ordres de magnitud més grans que els obtinguts a l’irradiar a 1100 nm (bandes Q). Aquestes observacions es poden explicar mitjançant la amplificació per ressonància deguda a la presència de transicions monofotòniques ressonants en la regió de les bandes Q. Els elevats valors de "delta" obtinguts per els tetrafenilporficèns estudiats junt a les principals característiques que aquestos presenten (elevat rendiment de formació d’oxigen singlet, estabilitat química i fotoquímica, absència de citotoxicitat,...) qualifiquen al TPPo y PdTPPo com a possibles fotosensibilitzadors per a Teràpia Fotodinàmica Bifotònica.