Asi1 is an inner nuclear membrane protein that restricts promoter access of two latent transcription factors

Boban, Mirta; Zargari, Arezou; Andréasson, Claes; Heessen, Stijn; Thyberg, Johan; Ljungdahl, Per O.

doi:10.1083/jcb.200601011

Cited by 44 publications

(77 citation statements)

References 49 publications

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“…Using immunofluorescence microscopy, we determined the intracellular location of full-length and processed forms of Stp1 and Stp2 in both wildtype and asi⌬1-3 strains. As in wild-type and asi1⌬ strains (27), Stp1 and Stp2 targeted to the nucleus only after induction with leucine (data not shown), indicating that Asi2 and Asi3 do not exert their regulatory affects by affecting bulk Stp1 and Stp2 localization. In summary, these results clearly indicate that the loss of Asi2 or Asi3 function enables full-length forms of Stp1 and Stp2 to induce SPS sensor-regulated genes, and provide support for the notion that Asi1, Asi2, and Asi3 function similarly to prevent SPS sensor gene expression in the absence of inducing amino acids.…”

Section: Asi Mutations Enable Signaling By Unprocessed Forms Of Stp1 mentioning

confidence: 98%

“…in the absence of extracellular amino acids. It does so by preventing transcription factors Stp1 and Stp2 from binding SPS sensor-regulated promoters (27). We anticipated that if the Asi2 and Asi3 proteins function similarly to Asi1, then strains carrying multiple mutations in ASI genes would display phenotypes similar to those of the single mutant strains.…”

Section: Asi2 and Asi3 Function Similar To Asi1 As Components Of The mentioning

confidence: 99%

“…The N-terminal domains possess two conserved sequence motifs, designated Regions I and II. Two parallel activities converge on Region I (27). The primary activity serves to anchor the unprocessed full-length forms to an undefined, cytoplasmic determinant, which prevents targeting of unprocessed factors to the nucleus.…”

Section: Asi Mutations Enable Signaling By Unprocessed Forms Of Stp1 mentioning

confidence: 99%

“…The fixed cells were washed in SP buffer (1.2 M sorbitol, 0.1 M potassium phosphate, pH 7.5), pelleted by centrifugation, dehydrated in graded ethanol (70 -100%), and embedded in LR White Resin (London Resin) by UV polymerization as described (27). Thin sections were cut on a Leica Ultracut and picked up on formvar-coated nickel grids.…”

Section: Determination Of Glycosylation Status and Membranementioning

confidence: 99%

“…We recently reported that ASI1 encodes an integral polytopic component of the inner nuclear membrane (27). The constitutive expression of SPS sensor-regulated genes in asi1⌬ mutants was traced to the ability of fulllength unprocessed forms of Stp1 and Stp2 to enter the nucleus, bind promoters, and induce transcription.…”

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confidence: 99%

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Inner Nuclear Membrane Proteins Asi1, Asi2, and Asi3 Function in Concert to Maintain the Latent Properties of Transcription Factors Stp1 and Stp2

Zargari

Boban

Heessen

et al. 2007

Journal of Biological Chemistry

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In yeast the homologous transcription factors Stp1 and Stp2 are synthesized as latent cytoplasmic precursors with N-terminal regulatory domains. In response to extracellular amino acids the regulatory domains are endoproteolytically excised by the plasma membrane-localized SPS sensor. The processed forms of Stp1 and Stp2 efficiently enter the nucleus and induce expression of amino acid permease genes. We recently reported that the inner nuclear membrane protein Asi1 is required to prevent unprocessed forms of Stp1 and Stp2, which ectopically enter the nucleus, from binding SPS sensor-regulated promoters. Here we show that Asi3, an Asi1 homolog, and Asi2 are integral proteins of the inner nuclear membrane that function in concert with Asi1. In cells lacking any of the three Asi proteins, unprocessed full-length forms of Stp1 and Stp2 constitutively induce SPS sensor-regulated genes. Our results demonstrate that the Asi proteins ensure the fidelity of SPS sensor signaling by maintaining the dormant, or repressed state, of gene expression in the absence of inducing signals. This study documents additional components of a novel mechanism controlling transcription in eukaryotic cells.In eukaryotes the nucleoplasm and cytoplasm are separated by the nuclear envelope. The nuclear envelope consists of two closely aligned bilayers, the inner and outer membranes, each with a unique set of resident proteins. The two nuclear membranes are joined at nuclear pore complexes, which function as channels that provide selective entry and exit routes across the nuclear envelope. Aside from rather detailed knowledge regarding the structure of nuclear pores, there is markedly little known regarding non-pore nuclear proteins (1). However, accumulating data indicate that nuclear envelope proteins participate in a variety of important processes including maintenance of nuclear architecture, chromatin organization, signaling, and gene expression (1-3). Significantly, mutations in genes encoding nuclear envelope proteins are linked to at least 15 inherited human diseases and syndromes (4, 5).In mammalian cells, nuclear lamins are involved in an extensive network of protein-protein interactions, including inner nuclear membrane proteins and transcriptional regulators, some of which bind DNA (3, 6). Although yeast cells lack lamin homologs (7), processes associated with the inner nuclear membrane have been shown to influence patterns of gene expression. For example, although silencing is not obligatorily linked to perinuclear anchoring (8), recruitment of chromatin to the nuclear periphery can facilitate gene repression (9). Evidence obtained using genome-wide approaches suggest that transcriptionally active regions of chromosomes localize to nuclear pore complexes (10, 11). Consistently, a number of actively expressed genes have been found to interact with the nucleoporin Nup2; the interactions occur at the promoter region of genes and appear to correlate with early events of gene expression (12, 13). Together findings in yeast and metazoan...

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Section: Asi Mutations Enable Signaling By Unprocessed Forms Of Stp1 mentioning

confidence: 98%

Section: Asi2 and Asi3 Function Similar To Asi1 As Components Of The mentioning

confidence: 99%

Section: Asi Mutations Enable Signaling By Unprocessed Forms Of Stp1 mentioning

confidence: 99%

Section: Determination Of Glycosylation Status and Membranementioning

confidence: 99%

mentioning

confidence: 99%

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Inner Nuclear Membrane Proteins Asi1, Asi2, and Asi3 Function in Concert to Maintain the Latent Properties of Transcription Factors Stp1 and Stp2

Zargari

Boban

Heessen

et al. 2007

Journal of Biological Chemistry

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Repair or destruction—an intimate liaison between ubiquitin ligases and molecular chaperones in proteostasis

2017

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Cellular differentiation, developmental processes, and environmental factors challenge the integrity of the proteome in every eukaryotic cell. The maintenance of protein homeostasis, or proteostasis, involves folding and degradation of damaged proteins, and is essential for cellular function, organismal growth, and viability 1, 2. Misfolded proteins that cannot be refolded by chaperone machineries are degraded by specialized proteolytic systems. A major degradation pathway regulating cellular proteostasis is the ubiquitin (Ub)/proteasome system (UPS), which regulates turnover of damaged proteins that accumulate upon stress and during aging. Despite a large number of structurally unrelated substrates, Ub conjugation is remarkably selective. Substrate selectivity is mainly provided by the group of E3 enzymes. Several observations indicate that numerous E3 Ub ligases intimately collaborate with molecular chaperones to maintain the cellular proteome. In this review, we provide an overview of specialized quality control E3 ligases playing a critical role in the degradation of damaged proteins. The process of substrate recognition and turnover, the type of chaperones they team up with, and the potential pathogeneses associated with their malfunction will be further discussed.

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Hypersensitive SSY1 mutations negatively influence transition to quiescence in yeast Saccharomyces cerevisiae

Marek

Opalek

Kałdon

et al. 2020

Yeast

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Most cells spend the majority of their life in the non‐proliferating, quiescent state. Transition to this state is crucial for microorganisms to survive long starvation periods and restart divisions afterwards. Experimental evolution allowed us to identify several mutation in genes that are presumably important for such transition in yeast cells. Most of these candidate genes belong to the SPS amino acid sensing pathway or to the SIR complex. We assembled these mutations on the ancestral strain background. Analysis of the quiescent/non‐quiescent cell ratio of the starved yeast populations confirmed the crucial role of SSY1, the primary receptor component of the SPS sensor, in transition to the Q state. The evolved SSY1 mutations increased yeast sensitivity to amino acid presence in the environment. This resulted in decreased quiescent cell fraction and a 5.14% increase of the total amino acid content in the starved populations. We discuss external amino acid sensing via the SPS pathway as one of the mechanisms influencing transition to quiescence.

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Asi1 is an inner nuclear membrane protein that restricts promoter access of two latent transcription factors

Cited by 44 publications

References 49 publications

Inner Nuclear Membrane Proteins Asi1, Asi2, and Asi3 Function in Concert to Maintain the Latent Properties of Transcription Factors Stp1 and Stp2

Inner Nuclear Membrane Proteins Asi1, Asi2, and Asi3 Function in Concert to Maintain the Latent Properties of Transcription Factors Stp1 and Stp2

Repair or destruction—an intimate liaison between ubiquitin ligases and molecular chaperones in proteostasis

Hypersensitive SSY1 mutations negatively influence transition to quiescence in yeast Saccharomyces cerevisiae

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