PMC:540003 JSONTXT

{"project":"2_test","denotations":[{"id":"15608285-10458604-76958361","span":{"begin":1673,"end":1674},"obj":"10458604"},{"id":"15608285-11084367-76958362","span":{"begin":1675,"end":1676},"obj":"11084367"},{"id":"15608285-12234915-76958363","span":{"begin":2065,"end":2066},"obj":"12234915"},{"id":"15608285-8177730-76958364","span":{"begin":2352,"end":2353},"obj":"8177730"},{"id":"15608285-12504020-76958365","span":{"begin":5083,"end":5084},"obj":"12504020"},{"id":"15608285-11752324-76958366","span":{"begin":6520,"end":6521},"obj":"11752324"},{"id":"15608285-10487866-76958367","span":{"begin":7666,"end":7667},"obj":"10487866"},{"id":"15608285-11724728-76958368","span":{"begin":7809,"end":7811},"obj":"11724728"},{"id":"15608285-10487866-76958369","span":{"begin":7887,"end":7888},"obj":"10487866"},{"id":"15608285-11724728-76958370","span":{"begin":8236,"end":8238},"obj":"11724728"},{"id":"15608285-11724736-76958370","span":{"begin":8236,"end":8238},"obj":"11724736"},{"id":"15608285-12136098-76958370","span":{"begin":8236,"end":8238},"obj":"12136098"},{"id":"15608285-15215408-76958370","span":{"begin":8236,"end":8238},"obj":"15215408"}],"text":"NPRD: Nucleosome Positioning Region Database \n\nAbstract\nNucleosome Positioning Region Database (NPRD), which is compiling the available experimental data on locations and characteristics of nucleosome formation sites (NFSs), is the first curated NFS-oriented database. The object of the database is a single NFS described in an individual entry. When annotating results of NFS experimental mapping, we pay special attention to several important functional characteristics, such as the relationship between type of gene activity and nucleosome positioning, the influence of non-histone proteins on nucleosome formation, type of the variant of nucleosome positioning (translational or rotational), indication of tissue types and states of cell activity, description of experimental methods used and accuracy of nucleosome position determination, and the results of applying theoretical and computer methods to the analysis of contextual and conformational DNA properties. At present, the NPRD database contains 438 entries and integrates the data described in 124 original papers. The database URL: http://srs6.bionet.nsc.ru/srs6/. Then click the button ‘Databank’ and open the link NUCLEOSOME.\n\nINTRODUCTION\nNucleosomes are the major structural elements of chromatin. Each nucleosome is formed by a 147 bp DNA fragment wrapped around an octamer composed of pairs of histone molecules of four types. In addition to DNA compacting, the most important function of nucleosomes is their interaction with the molecular components of the nucleus machineries involved in DNA replication, repair and recombination. The key role in gene transcription is also assigned to nucleosomes (1,2).\nChromatin is, as a rule, represented by regular arrays of nucleosomes. The factors determining the regularity of nucleosome location in vivo and in vitro are, first, the sequence-directed nucleosome positioning, determined by the interaction of nucleosome formation sites (NFSs) sequences with the histone octamer (3) and, second, their interaction with various non-histone proteins (4,5).\nSo far, the relative role of these factors in nucleosome positioning is vague. Presumably, this is first and foremost connected with insufficient volume of experimental data, preventing their systematization and formalization.\nThe database NUCLEOSOMAL DNA by Ioshikhes and Trifonov (6), comprising 143 entries, compiled the information about only the nucleosomal center positions and techniques used for the nucleosomal mapping; moreover, the information on types of nucleosome positioning and their relationship between transcription regulation and the state of gene activity was absent. In addition, the volume of this database and the degree of representation of the data on nucleosome organization in genomes of higher eukaryotes were evidently insufficient for large-scale research on nucleosome organization of the genomes and, in particular, estimation of the abilities of individual genomic regions to position nucleosomes.\nTo solve these problems, we are developing a curated NFS-oriented Nucleosome Positioning Region Database (NPRD). Along with a detailed description of NFS localization, including their mapping relative to the borders of genes and their structural elements, the database contains important functional characteristics: the relationship between types of gene activity and nucleosome positioning, the influence of non-histone proteins on nucleosome formation, occurrence of translational or rotational nucleosome positioning, indication of tissue types and states of cell activity, description of experimental methods used and the accuracy of nucleosome position determination, and the results of applying theoretical and computer methods to the analysis of contextual and conformational DNA properties. The database in question provides the possibility of formalized description and assessment of the contributions of the factors listed above to nucleosome positioning taking into account the available information about biologically significant characteristics of the regions considered.\nWe think that our database is important for developers of new computer methods of nucleosomal DNA analysis and recognition; and experimenters involved in transcription regulation and chromatin structure investigation.\n\nFORMAT OF THE NPRD DATABASE\nThe NPRD format developed allows for accumulating, integrating and systematizing miscellaneous experimental data on locations and characteristics of NFSs and detailed information about the other factors influencing nucleosome positioning, extracted from the published sources. Each NPRD entry corresponds to one annotated NFS. Below, we give a description of the fields in the order of their appearance (Table 1).\nAn example of an entry representing HNF-4-alpha gene proximal promoter nucleosome organization is given in Table 2. In active cells, the promoter and enhancer of this gene were occupied by positioned nucleosomes unlike in non-expressing cell lines, where positioning of nucleosomes was random. According to Hatzis and Talianidis model (7), formation of an active pre-initiation complex occurs in a step-by-step fashion: (i) poised or committed state (enhancer and promoter were occupied by the cognate DNA-binding proteins); (ii) recruitment of CBP and P/CAF (histone acetyltransferases), Brg-1 (chromatin remodeling protein) to the enhancer region and assembly of the RNA pol-II holoenzyme at the proximal promoter region; (iii) unidirectional movement of the DNA–protein complex formed on the enhancer along the intervening sequences and spreading of histone hyperacetylation and (iv) formation of a stable enhancer–promoter complex, hyperacetylation of nucleosomes located at the promoter, remodeling of the nucleosome located at the transcription start site and release of RNA pol-II from the promoter. Information on nucleosome positioning and its correlation with the gene activity is presented through the fields (Table 2): ‘Function’, ‘MainBounds’, ‘Comments’, ‘PosEvidence’, ‘NegEvidence’ and ‘KeyWords’.\n\nACCESS TO THE NPRD AND DATA RETRIEVAL TOOLS\nThe database URL: http://srs6.bionet.nsc.ru/srs6/. Then click the button ‘Databank’ and open the link NUCLEOSOME. Sequence Retrieval System (SRS) is used as a basic software tool for accessing the NPRD via the Internet; this provides efficient linking to the nucleotide sequences (EMBL/GenBank) and to the literature sources (PubMed). A system of hyperlinks integrates the NPRD with the informational system TRRD (8) (e.g. Table 2, field ‘Function’), allowing for a quick access to both the experimental information on the regulation of expression of a particular gene, whereto an NFS is localized, and the programs for computer analyses of regulatory sequences of the gene, providing users the possibility of additional data mining.\n\nDATABASE STATISTICS\nThe database contains 438 entries integrating the data of 124 original papers. Now, the Internet-accessible version contains 122 entries, constituting about one-third of the database volume.\nRepresentation of species is shown in Figure 1: sequences of higher eukaryotes constitute over 40% of the database; of them, 33% are mammalian genomes.\nFigure 2 illustrates the representation in the NPRD regions of genes and other functional components of the genomes. Note that the promoter regions constitute about a half of these regions, presumably indicating an increased interest of researchers to the relationship between nucleosome organization and transcription regulation.\n\nRESEARCH BASED ON DATA STORED IN THE NPRD\nWe have earlier designed an integrated information system Nucleosomal DNA Organization (9) (http://wwwmgs.bionet.nsc.ru/mgs/gnw/nucleosom/), comprising, along with NPRD, RECON program for nucleosome formation potential prediction (10) and NFS recognition by DNA conformational and physicochemical properties (9). Both programs were trained on NFS data later included in the NPRD dataset. Using the software package RECON, we have carried out the computer analysis of several classes of genome sequences: promoters of various classes, enhancers, coding and non-coding parts of genes, areas of splicing sites and sites of an insert of mobile genetic elements (10–15).\nThe volume of information, compiled in the NPRD, gives the possibility to study contextual characteristics of NFSs, increase the efficiency of their identification in genomic sequences and perform a more detailed research into nucleosome organization of genomes.\n\nFUTURE DEVELOPMENTS\nThe database NPRD is being constantly developed and supplemented with new experimental data from the available literature sources. We are planning to update the database annually. Concurrently, its integration with the existing databases and its search capabilities are being constantly improved. "}