Transcriptional activators interact with multisubunit coactivators that modify chromatin structure or recruit the general transcriptional machinery to their target genes. Budding yeast cells respond to amino acid starvation by inducing an activator of amino acid biosynthetic genes, Gcn4p. We conducted a comprehensive analysis of viable mutants affecting known coactivator subunits from the Saccharomyces Genome Deletion Project for defects in activation by Gcn4p in vivo. The results confirm previous findings that Gcn4p requires SAGA, SWI/SNF, and SRB mediator (SRB/MED) and identify key nonessential subunits of these complexes required for activation. Among the numerous histone acetyltransferases examined, only that present in SAGA, Gcn5p, was required by Gcn4p. We also uncovered a dependence on CCR4-NOT, RSC, and the Paf1 complex. In vitro binding experiments suggest that the Gcn4p activation domain interacts specifically with CCR4-NOT and RSC in addition to SAGA, SWI/SNF, and SRB/MED. Chromatin immunoprecipitation experiments show that Mbf1p, SAGA, SWI/SNF, SRB/MED, RSC, CCR4-NOT, and the Paf1 complex all are recruited by Gcn4p to one of its target genes (ARG1) in vivo. We observed considerable differences in coactivator requirements among several Gcn4p-dependent promoters; thus, only a subset of the array of coactivators that can be recruited by Gcn4p is required at a given target gene in vivo.Eukaryotic activator proteins stimulate transcription by binding to their target genes and carrying out two general functions: (i) altering the locations or structures of nucleosomes and (ii) recruiting TATA-binding protein (TBP), other general transcription factors (GTFs), and RNA polymerase II (RNA PolII) to the promoter. Most activators carry out these functions indirectly by recruiting multisubunit complexes, collectively called coactivators (39,70,90). One class of coactivators uses ATP hydrolysis to displace nucleosomes and thereby expose or obscure protein binding sites in the promoter (91,124). Each of the nucleosome remodeling complexes of Saccharomyces cerevisiae, known as SWI/SNF, RSC, ISW1, and ISW2, contains a different subunit harboring the ATPase activity of the complex (reviewed in references 70 and 91). Although each has been implicated in transcriptional activation in vivo (5,38,51,85,123), only the nonessential SWI/SNF complex has been shown to interact physically with activators (93, 139) and be recruited to a promoter for nucleosome remodeling and transcriptional activation in vitro (45,96,139). Recruitment of the SWI/SNF complex by yeast activators has also been demonstrated in living yeast cells by chromatin immunoprecipitation (ChIP) assays (24, 126).Another class of coactivators alters chromatin structure by acetylation of lysines in the amino-terminal tails of histones. This modification destabilizes higher-order chromatin structure (116) and also may stimulate binding of other coactivator proteins containing a bromodomain (9,91,120,135). The SAGA complex is the best-characterized yeast coactivato...

The Srb mediator is an important transcriptional coactivator for Gcn4p in the yeast Saccharomyces cerevisiae. We show that three subunits of the Gal11/tail domain of mediator, Gal11p, Pgd1p, and Med2p, and the head domain subunit Srb2p make overlapping contributions to the interaction of mediator with recombinant Gcn4p in vitro. Each of these proteins, along with the tail subunit Sin4p, also contributes to the recruitment of mediator by Gcn4p to target promoters in vivo. We found that Gal11p, Med2p, and Pgd1p reside in a stable subcomplex in sin4⌬ cells that interacts with Gcn4p in vitro and that is recruited independently of the rest of mediator by Gcn4p in vivo. Thus, the Gal11p/Med2p/Pgd1p triad is both necessary for recruitment of intact mediator and appears to be sufficient for recruitment by Gcn4p as a free subcomplex. The med2⌬ mutation impairs the recruitment of TATA binding protein (TBP) and RNA polymerase II to the promoter and the induction of transcription at ARG1, demonstrating the importance of the tail domain for activation by Gcn4p in vivo. Even though the Gal11p/Med2p/Pgd1p triad is the only portion of Srb mediator recruited efficiently to the promoter in the sin4⌬ strain, this mutant shows high-level TBP recruitment and wild-type transcriptional induction at ARG1. Hence, the Gal11p/Med2p/Pgd1p triad may contribute to TBP recruitment independently of the rest of mediator.

BackgroundThe discovery of genetically distinct hantaviruses in shrews (Order Soricomorpha, Family Soricidae) from widely separated geographic regions challenges the hypothesis that rodents (Order Rodentia, Family Muridae and Cricetidae) are the primordial reservoir hosts of hantaviruses and also predicts that other soricomorphs harbor hantaviruses. Recently, novel hantavirus genomes have been detected in moles of the Family Talpidae, including the Japanese shrew mole (Urotrichus talpoides) and American shrew mole (Neurotrichus gibbsii). We present new insights into the evolutionary history of hantaviruses gained from a highly divergent hantavirus, designated Nova virus (NVAV), identified in the European common mole (Talpa europaea) captured in Hungary.Methodology/Principal FindingsPair-wise alignment and comparison of the full-length S- and L-genomic segments indicated moderately low sequence similarity of 54–65% and 46–63% at the nucleotide and amino acid levels, respectively, between NVAV and representative rodent- and soricid-borne hantaviruses. Despite the high degree of sequence divergence, the predicted secondary structure of the NVAV nucleocapsid protein exhibited the characteristic coiled-coil domains at the amino-terminal end, and the L-segment motifs, typically found in hantaviruses, were well conserved. Phylogenetic analyses, using maximum-likelihood and Bayesian methods, showed that NVAV formed a distinct clade that was evolutionarily distant from all other hantaviruses.ConclusionsNewly identified hantaviruses harbored by shrews and moles support long-standing virus-host relationships and suggest that ancestral soricomorphs, rather than rodents, may have been the early or original mammalian hosts.

Recently identified hantaviruses harbored by shrews and moles (order Soricomorpha) suggest that other mammals having shared ancestry may serve as reservoirs. To investigate this possibility, archival tissues from 213 insectivorous bats (order Chiroptera) were analyzed for hantavirus RNA by RT-PCR. Following numerous failed attempts, hantavirus RNA was detected in ethanol-fixed liver tissue from two banana pipistrelles (Neoromicia nanus), captured near Mouyassué village in Côte d'Ivoire, West Africa, in June 2011. Phylogenetic analysis of partial L-segment sequences using maximum-likelihood and Bayesian methods revealed that the newfound hantavirus, designated Mouyassué virus (MOUV), was highly divergent and basal to all other rodent-and soricomorph-borne hantaviruses, except for Nova virus in the European common mole (Talpa europaea). Full genome sequencing of MOUV and further surveys of other bat species for hantaviruses, now underway, will provide critical insights into the evolution and diversification of hantaviruses.Keywords: Hantavirus, Bat, Phylogeny, Côte d'Ivoire, Africa FindingsDiscovery of phylogenetically divergent hantaviruses in shrews and moles (order Soricomorpha, family Soricidae and Talpidae) [1][2][3][4][5][6][7][8][9][10][11][12][13] raises the possibility that rodents (order Rodentia, family Muridae and Cricetidae) may not be the principal or primordial reservoirs. Moreover, newfound hantaviruses harbored by soricomorphs of multiple species, distributed in widely separated geographic regions across four continents, suggest that their host diversity may be far more expansive than previously assumed. Specifically, other mammals having shared ancestry or ecosystems with soricomorphs may serve as reservoirs and may be important in the evolutionary history and diversification of hantaviruses. In particular, bats (order Chiroptera) may be potential reservoirs by virtue of their rich diversity and vast geographical range, as well as their demonstrated ability to host myriad medically important, disease-causing viruses [14][15][16][17][18]. Surprisingly little attention, however, has been paid to this possibility.As in our previous investigations on the spatial and temporal distribution of hantaviruses in soricomorphs [2-13], we relied on the availability of archival tissues. Using the PureLink Micro-to-Midi total RNA purification kit (Invitrogen, San Diego, CA), total RNA was extracted from 168 frozen and 45 ethanol-fixed liver and other visceral tissues of 213 insectivorous bats (representing 13 genera), collected during May 1981 to June 2011 in Asia, Africa and the Americas (Table 1). cDNA was then prepared with the SuperScript III FirstStrand Synthesis System (Invitrogen) using random hexamers, and PCR was performed as described previously, using an extensive panel of oligonucleotide primers, designed on conserved genomic sequences of rodentand soricomorph-borne hantaviruses [2][3][4][5][6][7][8][9][10][11][12][13]19,20]. Each reaction mixture contained 250 μ dNTP, 2 mM MgCl 2 , 1 U Ampl...

A genetically distinct hantavirus, designated Oxbow virus (OXBV), was detected in tissues of an American shrew mole (Neurotrichus gibbsii), captured in Gresham, Oregon, in September 2003. Pairwise analysis of full-length S- and M- and partial L-segment nucleotide and amino acid sequences of OXBV indicated low sequence similarity with rodent-borne hantaviruses. Phylogenetic analyses using maximum-likelihood and Bayesian methods, and host-parasite evolutionary comparisons, showed that OXBV and Asama virus, a hantavirus recently identified from the Japanese shrew mole (Urotrichus talpoides), were related to soricine shrew-borne hantaviruses from North America and Eurasia, respectively, suggesting parallel evolution associated with cross-species transmission.