Deficient in DNA Methylation 1 (DDM1) protein is required to maintain the DNA methylation status of Arabidopsis thaliana. DDM1 is a member of the broad SWI2/SNF2 protein family. Because of its ...phylogenetic position, DDM1 has been speculated to act as a chromatin-remodeling factor. Here we used a purified recombinant DDM1 protein to investigate whether it can remodel chromatin in vitro. We show that DDM1 is an ATPase stimulated by both naked and nucleosomal DNA. DDM1 binds to the nucleosome and promotes chromatin remodeling in an ATP-dependent manner. Specifically, it induces nucleosome repositioning on a short DNA fragment. The enzymatic activity of DDM1 is not affected by DNA methylation. The relevance of these findings to the in vivorole of DDM1 is discussed.
Paramutation involves homologous sequence communication that leads to meiotically heritable transcriptional silencing. We demonstrate that mop2 (mediator of paramutation2), which alters paramutation ...at multiple loci, encodes a gene similar to Arabidopsis NRPD2/E2, the second-largest subunit of plant-specific RNA polymerases IV and V. In Arabidopsis, Pol-IV and Pol-V play major roles in RNA-mediated silencing and a single second-largest subunit is shared between Pol-IV and Pol-V. Maize encodes three second-largest subunit genes: all three genes potentially encode full length proteins with highly conserved polymerase domains, and each are expressed in multiple overlapping tissues. The isolation of a recessive paramutation mutation in mop2 from a forward genetic screen suggests limited or no functional redundancy of these three genes. Potential alternative Pol-IV/Pol-V-like complexes could provide maize with a greater diversification of RNA-mediated transcriptional silencing machinery relative to Arabidopsis. Mop2-1 disrupts paramutation at multiple loci when heterozygous, whereas previously silenced alleles are only up-regulated when Mop2-1 is homozygous. The dramatic reduction in b1 tandem repeat siRNAs, but no disruption of silencing in Mop2-1 heterozygotes, suggests the major role for tandem repeat siRNAs is not to maintain silencing. Instead, we hypothesize the tandem repeat siRNAs mediate the establishment of the heritable silent state-a process fully disrupted in Mop2-1 heterozygotes. The dominant Mop2-1 mutation, which has a single nucleotide change in a domain highly conserved among all polymerases (E. coli to eukaryotes), disrupts both siRNA biogenesis (Pol-IV-like) and potentially processes downstream (Pol-V-like). These results suggest either the wild-type protein is a subunit in both complexes or the dominant mutant protein disrupts both complexes. Dominant mutations in the same domain in E. coli RNA polymerase suggest a model for Mop2-1 dominance: complexes containing Mop2-1 subunits are non-functional and compete with wild-type complexes.
Energy-dependent nucleosome remodeling emerges as a key process endowing chromatin with dynamic properties. However, the principles by which remodeling ATPases interact with their nucleosome ...substrate to alter histone-DNA interactions are only poorly understood. We have identified a substrate recognition domain in the C-terminal half of the remodeling ATPase ISWI and determined its structure by X-ray crystallography. The structure comprises three domains, a four-helix domain with a novel fold and two α-helical domains related to the modules of c-Myb, SANT and SLIDE, which are linked by a long helix. An integrated structural and functional analysis of these domains provides insight into how ISWI interacts with the nucleosomal substrate.
Paramutation is the ability of specific DNA sequences to communicate in trans to establish meiotically heritable expression states. Paramutation at the maize b1 locus is mediated by seven unique ...noncoding transcribed tandem repeats of 853 bp that are required to establish and maintain the meiotically heritable expression and distinct chromatin states associated with b1 paramutation. In this study, we report the identification of a CXC-domain protein CBBP (CXC domain b1-repeat binding protein) that binds to a defined region within the b1 tandem repeat sequence in vivo and in vitro. When CBBP is expressed from a transgene in maize, it can induce a silent state at the b1 locus that is heritable in progeny no longer containing the transgene, and the silent epiallele is capable of silencing an active epiallele, characteristic of paramutation. Accumulation of the CBBP protein correlates with b1 silencing in transgenic and nontransgenic plants. The ability of CBBP to form multimers and to bind to the b1 tandem repeats suggests a model for counting the number of b1 repeats. In contrast to previously identified proteins involved in paramutation, CBBP does not share similarity to the known components of the Arabidopsis RNAi heterochromatin silencing pathway. Thus, this study defines another class of protein that is involved in heritable gene silencing.
In recent years, the countries of the Europe and Central Asia (ECA) Region have experienced a marked decline in the interest of international private operators and investors in municipal ...infrastructure projects, in line with the trend experienced in other emerging markets. The objective of this paper is to explore the possible innovative elements of a Public-Private Partnership (PPP) in an effort to rekindle the sagging private finance interest in municipal infrastructure in the ECA Region. The contemplated PPP model would involve government, municipalities, Local Infrastructure Investment Trusts, private equity funds and/or turnaround advisors, and International Financial Institutions.
Epigenetic mechanisms maintain gene expression states through mitotic and sometimes meiotic cell divisions. Paramutation is an extreme example of epigenetic processes. Not only an established ...expression state is transmitted through meiosis to the following generations but also an information transfer occurs between alleles and leads to heritable changes in expression state. As a consequence the expression states can rapidly propagate in population, violating Mendelian genetics. Recent findings unraveled an essential role for siRNA‐dependent processes in paramutation. Despite significant progress, the overall picture is still puzzling and many important questions remain to be answered. WIREs RNA 2011 2 863–874 DOI: 10.1002/wrna.97
Regulatory RNAs/RNAi/Riboswitches > RNAi: Mechanisms of Action
RNA in Disease and Development > RNA in Disease
RNA in Disease and Development > RNA in Development
Polish Fixed-income Securities Market Noel, Michel; Akamatsu, Noritaka; Brzeski, Wladyslaw Jan ...
2006, 11-29-2006, 2007, 20070101, Letnik:
91
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This book analyzes the recent evolution of the Polish fixedincome securities market, including the money market, the government bond market, and the non-government bond market, focusing in particular ...on the sub-national bond market. The book examines key policy challenges facing the development of the sector, including policies to: stimulate the development of the classic repo market, increase the reliability of the government bond yield curve, stimulate the overall development of the non-government bond market, and reform the legal and regulatory framework for local government borrowing.
This research provides new insight into the evolution of an urban land market in a centrally planned economy undergoing transformation. In Poland, land use decisions were previously made ...administratively but during the time frame of analysis from early 1993 to late 1999 were being driven by market forces. The results of this initial study are that the fit of the estimated land value functions declines as time passes and that in most cases the slope of each of the land value functions becomes steeper as time passes. We attribute the latter result to real relative increases in transportation and opportunity costs. Separately, the availability of infrastructure is shown to have significant impact on lot value.
Studies in organisms belonging to different eukaryotic kingdoms have revealed that the structural state of chromatin is controlled by interactions of DNA, small RNAs and specific proteins, linked to ...a self-reinforcing complex network of biochemical activities involving histone and DNA modifications and ATP-dependent nucleosome remodeling. However, these findings must now be reinterpreted in light of the recent discovery of the highly dynamic character of interphase chromosomes exemplified by the constant flux of enzymatic and structural proteins through both eu- and heterochromatin and by short- and long-range chromosome movements in the nucleus. The available data on chromosome organization in
Arabidopsis thaliana and links between proteins influencing chromatin structure and DNA and histone modifications documented in this model plant provide strong supportive evidence for the dynamic nature of chromosomes.
We examine commercial land markets in Krakow, Poland over a 10‐year period of transition from socialist management to a market economy. We explore the spatial and temporal evolution of land prices ...over this period. In particular, we are interested in identifying trends toward or away from centrality, and in discovering whether or not these trends acted on the city center alone or over a set of centers. The data set we employ is uniquely appropriate for this purpose as the densifying force of “highest‐and‐best” use—typically found in market‐oriented cities—was absent under four decades of socialist planning, leaving undeveloped land scattered throughout the city. Free of quality control issues associated with disentangling the value of land from properties in which land and structures are bundled, the data offer a clean assessment of land prices within an urban area. We employ a novel, iterative approach to identify pricing centers—“nodes” of similarly sized residuals—which we interpret as evidence of omitted spatial amenities. Using this approach, we find that the price gradient in Krakow evolved toward concentration, but concentration in several centers rather than in just one. We find that the exclusion of proximity to these centers leads to biased coefficients in the hedonic regressions; we also find that the majority of the apparent spatial autocorrelation in the aspatial regressions results from the omission of proximity to these centers.
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