Most nucleosomes are well-organized at the 5Ј ends of S. cerevisiae genes where "−1" and "+1" nucleosomes bracket a nucleosome-free promoter region (NFR). How nucleosomal organization is specified by the genome is less clear. Here we establish and inter-relate rules governing genomic nucleosome organization by sequencing DNA from more than one million immunopurified S. cerevisiae nucleosomes (displayed at http://atlas.bx.psu.edu/). Evidence is presented that the organization of nucleosomes throughout genes is largely a consequence of statistical packing principles. The genomic sequence specifies the location of the −1 and +1 nucleosomes. The +1 nucleosome forms a barrier against which nucleosomes are packed, resulting in uniform positioning, which decays at farther distances from the barrier. We present evidence for a novel 3Ј NFR that is present at >95% of all genes. 3Ј NFRs may be important for transcription termination and anti-sense initiation. We present a high-resolution genome-wide map of TFIIB locations that implicates 3Ј NFRs in gene looping.

The nucleosome is the fundamental building block of eukaryotic chromosomes. Access to genetic information encoded in chromosomes is dependent on the position of nucleosomes along the DNA. Alternative locations just a few nucleotides apart can have profound effects on gene expression. Yet the nucleosomal context in which chromosomal and gene regulatory elements reside remains ill-defined on a genomic scale. Here we sequence the DNA of 322,000 individual Saccharomyces cerevisiae nucleosomes, containing the histone variant H2A.Z, to provide a comprehensive map of H2A.Z nucleosomes in functionally important regions. With a median 4-base-pair resolution, we identify new and established signatures of nucleosome positioning. A single predominant rotational setting and multiple translational settings are evident. Chromosomal elements, ranging from telomeres to centromeres and transcriptional units, are found to possess characteristic nucleosomal architecture that may be important for their function. Promoter regulatory elements, including transcription factor binding sites and transcriptional start sites, show topological relationships with nucleosomes, such that transcription factor binding sites tend to be rotationally exposed on the nucleosome surface near its border. Transcriptional start sites tended to reside about one helical turn inside the nucleosome border. These findings reveal an intimate relationship between chromatin architecture and the underlying DNA sequence it regulates.

Comparative genomics of nucleosome positions provides a powerful means for understanding how the organization of chromatin and the transcription machinery co-evolve. Here we produce a high resolution reference map of H2A.Z and bulk nucleosome locations across the genome of the fly D. melanogaster, and compare it to that from the yeast S. cerevisiae. Like Saccharomyces, Drosophila nucleosomes are organized around active transcription start sites in a canonical −1, NFR (nucleosome-free region), +1 arrangement. However, Drosophila does not incorporate H2A.Z into the −1 nucleosome and does not bury its transcriptional start site in the +1 nucleosome. At thousands of genes, RNA polymerase II engages the +1 nucleosome and pauses. How the transcription initiation machinery contends with the +1 nucleosome appears to be fundamentally different between lower and higher eukaryotes.Knowledge of the precise location of nucleosomes in a genome is essential in order to understand the context in which chromosomal processes such as transcription and DNA replication operate. A common theme to emerge from recent genome-wide maps of nucleosome locations is a general deficiency of nucleosomes in promoter regions and an enrichment of certain histone modifications towards the 5′ end of genes [1][2][3][4][5][6][7] . A high resolution genomic map of nucleosome locations in the budding yeast S. cerevisiae has further revealed Correspondence and request for material should be addressed to B.F.P. (bfp2@psu.edu). * These authors contributed equally to this work.Author Information Sequence data deposition is through NCBI Trace Archives TI SRA000283, Sequencing Center = "CCGB", and microarray deposition through ArrayExpress, Accession numbers E-MEXP-1515 and -1519. Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interest.Author Contributions T.M. prepared and purified the nucleosomes including Pol II-bound nucleosomes; C.J. analyzed the nucleosome mapping data and its relationship to other genomic features; I.P.I. performed computational analyses related to nucleosome positioning sequences; X.L. conducted ChIP-chip on Pol II; B.J.V. conducted ChIP-chip on nucleosome-Pol II interactions; S.J.Z. provided bioinformatics support; L.T. constructed libraries and sequenced nucleosomal DNA; J.Q. mapped sequencing reads to the yeast genome; RG provided H2A.Z antibodies; SCS directed the DNA sequencing phase; DSG directed embryo preparations and helped interpret the data; I.A. developed computational approaches to derive nucleosome maps from the read locations and developed the associated browser; B.F.P. directed the project, interpreted the data, and wrote the paper. S6). Those 112,750 nucleosomes detected three or more times were further analyzed, although patterns were identical when all nucleosomes were analyzed. The internal median error of the data was 4 bp (Fig. S7). H2A.Z nucleosomes were predominantly distributed at 175 bp intervals from the TSS (compared to 165 ...

SUMMARY Hundreds of different proteins regulate and implement transcription in Saccharomyces. Yet their inter-relationships have not been investigated on a comprehensive scale. Here we determined the genome-wide binding locations of 200 transcription-related proteins, under normal and acute heat shock conditions. This study distinguishes binding between distal versus proximal promoter regions as well as the 3' ends of genes for nearly all mRNA and tRNA genes. This study reveals 1) a greater diversity and specialization of regulation associated with the SAGA transcription pathway compared to the TFIID pathway, 2) new regulators enriched at tRNA genes, 3) a global co-occupancy network of >20,000 unique regulator combinations that show a high degree of regulatory interconnections among lowly-expressed genes, 4) regulators of the SAGA pathway located largely distal to the core promoter and regulators of the TFIID pathway located proximally, and 5) distinct mobilization of SAGA- versus TFIID-linked regulators during acute heat shock.

Temperate phages are common and prophages are abundant residents of sequenced bacterial genomes. Mycobacteriophages are viruses infecting mycobacterial hosts including Mycobacterium tuberculosis and Mycobacterium smegmatis, encompass substantial genetic diversity, and are commonly temperate. Characterization of ten Cluster N temperate mycobacteriophages reveals at least five distinct prophage-expressed viral defense systems that interfere with infection of lytic and temperate phages that are either closely-related (homotypic defense) or unrelated (heterotypic defense). Target specificity is unpredictable, ranging from a single target phage to one-third of those tested. The defense systems include a single-subunit restriction system, a heterotypic exclusion system, and a predicted (p)ppGpp synthetase, which blocks lytic phage growth, promotes bacterial survival, and enables efficient lysogeny. The predicted (p)ppGpp synthetase coded by the Phrann prophage defends against phage Tweety infection, but Tweety codes for a tetrapeptide repeat protein, gp54, that acts as a highly effective counter-defense system. Prophage-mediated viral defense offers an efficient mechanism for bacterial success in host-virus dynamics, and counter-defense promotes phage co-evolution.