Genome-wide studies in S. cerevisiae reveal that the transcriptome includes numerous antisense RNAs as well as intergenic transcripts regulated by the exosome component Rrp6. We observed that upon the loss of Rrp6 function, two PHO84 antisense transcripts are stabilized, and PHO84 gene transcription is repressed. Interestingly, the same phenotype is observed in wild-type cells during chronological aging. Epistasis and chromatin immunoprecipitation experiments indicate that the loss of Rrp6 function is paralleled by the recruitment of Hda1 histone deacetylase to PHO84 and neighboring genes. However, histone deacetylation is restricted to PHO84, suggesting that Hda1 activity depends on antisense RNA. Accordingly, the knockdown of antisense production prevents PHO84 gene repression, even in the absence of Rrp6. Together, our data indicate that the stabilization of antisense transcripts results in PHO84 gene repression via a mechanism distinct from transcription interference and that the modulation of Rrp6 function contributes to gene regulation by inducing RNA-dependent epigenetic modifications.

Transcription activation of some Saccharomyces cerevisiae genes is paralleled by their repositioning to the nuclear periphery, but the mechanism underlying gene anchoring is poorly defined. We show that the nuclear pore complex-associated Mlp1p and the shuttling mRNA export receptor Mex67p contribute to the stable association of the activated GAL10 and HSP104 genes with the nuclear periphery. However, we find no obligatory link between gene positioning and gene expression. Furthermore, gene anchoring correlates with the cotranscriptional recruitment of Mex67p to transcribing genes. Notably, the association of Mex67p with chromatin is not mediated by RNA. Interestingly, a mutant GAL2 gene lacking the coding region is still able to recruit Mex67p upon transcriptional activation and to relocate to the nuclear periphery. Together these data suggest that, at least for GAL2, nascent messenger ribonucleoprotein does not play a major role in gene anchoring and that the early recruitment of Mex67p contributes to gene repositioning by virtue of an RNA-independent process.A growing number of recent studies point to a functional relationship between gene expression and nuclear organization of chromatin. Indeed, the nucleus is subdivided into spatially defined domains, and the nonrandom distribution of chromosomes within these domains is thought to regulate their transcriptional state (8,25). Notably, the nuclear periphery has first been viewed as a transcriptionally repressive zone. In Saccharomyces cerevisiae, telomeres and mating-type loci, consisting of silent chromatin, concentrate in nuclear peripheral regions (16), and artificial tethering of nonsilenced DNA to the envelope induces its repression (2). In particular, the nuclear pore complex (NPC) has been implicated in perinuclear gene silencing and maintenance of gene expression states. Indeed, loss of a subset of NPC components, including the nuclear basketanchored Mlp1p and Mlp2p, results in the activation of subtelomeric reporter genes (10,12,20). However, another study showed that artificial tethering of nuclear transport factors to a partially silenced mating-type locus allowed its expression. Thus, recruitment of genes to the nuclear periphery can also have important effects on their activation (24). Consistent with these observations, genome-wide analyses of NPC-bound loci identified preferential association of highly transcribed genes with the nuclear periphery. These studies also showed that transcriptional activation of genes induced by galactose or ␣-factor is accompanied by their relocation from the nuclear interior to the nuclear periphery (5, 6). INO1 gene activation is also paralleled by its repositioning to the periphery, and this relocation contributes to optimal INO1 gene expression (3).Importantly, recent studies pointed to a direct physical link between Sus1p, a component of the SAGA histone deacetylase coactivator complex, and the Sac3-Thp1 complex, which is part of the mRNA export machinery associated with pores (31). These data together suggest...

During transcription, proteins assemble sequentially with nascent RNA to generate a messenger ribonucleoprotein particle (mRNP). The THO complex and its associated Sub2p helicase are functionally implicated in both transcription and mRNP biogenesis but their precise function remains elusive. We show here that THO/Sub2p mutation leads to the accumulation of a stalled intermediate in mRNP biogenesis that contains nuclear pore components and polyadenylation factors in association with chromatin. Microarray analyses of genomic loci that are aberrantly docked to the nuclear pore in mutants allowed the identification of approximately 400 novel validated target genes that require THO /Sub2p for efficient expression. Our data strongly suggests that the THO complex/Sub2p function is required to coordinate events leading to the acquisition of export competence at a step that follows commitment to 3'-processing.

The opportunistic pathogen Pseudomonas aeruginosa responds to zinc, cadmium and cobalt by way of the CzcRS two-component system. In presence of these metals the regulatory protein CzcR induces the expression of the CzcCBA efflux pump, expelling and thereby inducing resistance to Zn, Cd and Co. Importantly, CzcR co-regulates carbapenem antibiotic resistance by repressing the expression of the OprD porin, the route of entry for these antibiotics. This unexpected co-regulation led us to address the role of CzcR in other cellular processes unrelated to the metal response. We found that CzcR affected the expression of numerous genes directly involved in the virulence of P. aeruginosa even in the absence of the inducible metals. Notably the full expression of quorum sensing 3-oxo-C12-HSL and C4-HSL autoinducer molecules is impaired in the absence of CzcR. In agreement with this, the virulence of the czcRS deletion mutant is affected in a C. elegans animal killing assay. Additionally, chromosome immunoprecipitation experiments allowed us to localize CzcR on the promoter of several regulated genes, suggesting a direct control of target genes such as oprD, phzA1 and lasI. All together our data identify CzcR as a novel regulator involved in the control of several key genes for P. aeruginosa virulence processes.

Transcription activation of some yeast genes correlates with their repositioning to the nuclear pore complex (NPC). The NPC-bound Mlp1 and Mlp2 proteins have been shown to associate with the GAL1 gene promoter and to maintain Ulp1, a key SUMO protease, at the NPC. Here, we show that the release of Ulp1 from the NPC increases the kinetics of GAL1 derepression, whereas artificial NPC anchoring of Ulp1 in the Δmlp1/2 strain restores normal GAL1 regulation. Moreover, artificial tethering of the Ulp1 catalytic domain to the GAL1 locus enhances the derepression kinetics. Our results also indicate that Ulp1 modulates the sumoylation state of Tup1 and Ssn6, two regulators of glucose-repressed genes, and that a loss of Ssn6 sumoylation correlates with an increase in GAL1 derepression kinetics. Altogether, our data highlight a role for the NPC-associated SUMO protease Ulp1 in regulating the sumoylation of gene-bound transcription regulators, positively affecting transcription kinetics in the context of the NPC.

SummaryIt is now well established that the position of a gene within the nucleus can influence the level of its activity. So far, special emphasis has been placed on the nuclear envelope (NE) as a transcriptionally silent nuclear sub-domain. Recent work, however, indicates that peripheral localization is not always associated with repression, but rather fulfills a dual function in gene expression. In particular, in the yeast Saccharomyces cerevisiae, a large number of highly expressed genes and activated inducible genes preferentially associate with nuclear pore complexes (NPCs), a process that is mediated by transient interactions between the transcribed locus and the NPC. Recent studies aimed at unraveling the molecular basis of this mechanism have revealed that maintenance of genes at the NPC involves multiple tethers at different steps of gene expression. These observations are consistent with tight interconnections between transcription, mRNA processing and export into the cytoplasm, and highlight a role for the NPC in promoting and orchestrating the gene expression process. In this Commentary, we discuss the factors involved in active gene anchoring to the NPC and the diverse emerging roles of the NPC environment in promoting gene expression, focusing on yeast as a model organism.

Pseudomonas entomophila is unique among Pseudomonas species in being able to activate a systemic immune response in both Drosophila larvae and adults. It has been subsequently shown that oral infections with high doses of this bacterium are highly pathogenic to Drosophila and cause massive destruction of the Drosophila gut epithelium. Besides Drosophila, P. entomophila was able to kill other insects from at least three different orders, suggesting that it has a potentially wide host range and making it a promising model for the study of host pathogen interactions and for the development of bio-control agents against insect pests. In order to unravel the features contributing to P. entomophila's pathogenic properties, its complete genome was sequenced and genetic screens were performed to identify virulence factors encoded by this bacterium. The aim of this chapter is to review the current knowledge we have on this bacterium with a particular focus on the pathogenesis it induces, its virulence effectors and their genetic regulation.

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