Disease relevance of GAP1

• However, immunoblot and permease assays indicated that Gap1 in the rsp5 mutant remained stable and active on the plasma membrane probably with no ubiquitination, leading to AZC accumulation and hypersensitivity [1].
• Exploiting this toxicity, we isolated gap1 alleles deficient in transport of a subset of amino acids [2].

High impact information on GAP1

• Here, we report the identification of a conserved sorting complex for Gap1p, named the GTPase-containing complex for Gap1p sorting in the endosomes (GSE complex), which is required for proper sorting of Gap1p from the late endosome for eventual delivery to the plasma membrane [3].
• Together, these studies provide evidence that the GSE complex has a key role in trafficking Gap1p out of the endosome and may serve as coat proteins in this process [3].
• We show that the GGA coat proteins bind directly to ubiquitin through their GAT domain and demonstrate that this interaction is required for the ubiquitin-dependent sorting of the Gap1 amino acid transporter from the TGN to endosomes [4].
• Further, we show that a sublethal concentration of rapamycin mimics the Gap1p sorting defect of an lst8 mutant [5].
• Here, we report that the Gap1p sorting defect in the lst8-1 mutant results from derepression of Rtg1/3p activity and the subsequent accumulation of high levels of intracellular amino acids, which signal Gap1p sorting to the vacuole [5].

Biological context of GAP1

• The data presented here are compatible with this negative control operating either at the transcriptional or at a post-transcriptional level of the GAP1 gene expression [6].
• Frameshift mutations in the GAP1 locus, and conditional, thermosensitive, mutations in the NPR1 locus were also obtained [6].
• When poly-ubiquitination through Lys63 is blocked, the Gap1p permease still undergoes NH4+-induced down-regulation, but to a lesser extent [7].
• Uptake by Saccharomyces cerevisiae of the sulphur-containing amino acid L-cysteine was found to be non-saturable under various conditions, and uptake kinetics suggested the existence of two or more transport systems in addition to the general amino-acid permease, Gap1p [8].
• In Saccharomyces cerevisiae the general amino acid (GAP1) permease catalyses active transport of apparently all amino acids across the plasma membrane [9].

Anatomical context of GAP1

• Following an ammonia pulse, the expression of GAP1, PUT4 and GDH1 decreased while the intracellular glutamine concentration remained constant, both in the cytoplasm and in the vacuole [10].
• The activities at the Golgi of recombinant GAP1 as well as coatomer-depleted fractions from rat brain cytosol resembled those observed in the presence of liposomes; however, unlike in liposomes, GAP activities on Golgi membranes were approximately doubled upon addition of coatomer [11].
• A non-flocculent strain of Saccharomyces cerevisiae was transformed with the GAP1 gene which encodes p37, a GAPDH-like protein present in the cell wall of Kluyveromyces marxianus flocculent cells [12].
• Hence the GAP1 gene encodes a protein with characteristics typical of integral membrane proteins translocating ligants across cellular membranes [13].
• In yeast cells grown on either ammonia or urea medium, the general amino acid permease (Gap1p) is transported from the Golgi complex to the plasma membrane, whereas, in cells grown on glutamate medium, Gap1p is transported from the Golgi to the vacuole [14].

Associations of GAP1 with chemical compounds

• In yeast GABA is also incorporated by the general amino acid permease (GAP1) and the specific proline permease (PUT4) [15].
• Deletion of the general amino acid permease gene GAP1 abolishes uptake of L-citrulline in Saccharomyces cerevisiae, resulting in the inability to grow on L-citrulline as sole nitrogen source [16].
• Leucine uptake by Saccharomyces cerevisiae is mediated by three transport systems, the general amino acid transport system (GAP), encoded by GAP1, and two group-specific systems (S1 and S2), which also transport isoleucine and valine [17].
• This report shows that inactivation by NH4+ of the Gap1 permease is accompanied by its degradation [18].
• Addition of NH4+ triggers rapid poly-ubiquitination of Gap1p, the poly-ubiquitin chains being specifically formed by linkage through the lysine 63 residue of ubiquitin [7].

Physical interactions of GAP1

• We show here that mutant Gap1 permeases affected in these sequences still bind Ub [19].

Enzymatic interactions of GAP1

• Finally, Gap1 is phosphorylated in NPR1 cells, but this phosphorylation is not strictly dependent on Npr1 [20].

Regulatory relationships of GAP1

• We show that Npi3 is required for NH4+-induced down-regulation of Gap1, and particularly for efficient ubiquitination of the permease [21].
• Our results reveal a novel role of ubiquitin in the control of Gap1 trafficking, i.e. direct sorting from the late secretory pathway to the vacuole [22].
• We conclude that Dot4p is involved in posttranscriptionally regulating Gap1p, and possibly other transporters as well [23].
• The Npr1 kinase controls biosynthetic and endocytic sorting of the yeast Gap1 permease [20].
• This vector is based on the pY37 previously described, harbouring a S11 Kluyveromyces origin of replication, and the expression of GAP1 is under the control of GAL1 [24].

Other interactions of GAP1

• Furthermore, our results suggest that TAT2 stability and sorting are controlled by the TOR signaling pathway, and regulated inversely to that of GAP1 [25].
• NPl1, an essential yeast gene involved in induced degradation of Gap1 and Fur4 permeases, encodes the Rsp5 ubiquitin-protein ligase [18].
• Here we report that yet another protein, Npi3, is involved in the regulation of Gap1 trafficking [21].
• There is still a leucine-inducible increase in branched-chain amino acid uptake in a delta gap1 delta bap2 strain, indicating that BAP2 shares leucine induction with at least one remaining branched-chain amino acid-transporting permease [26].
• To study the effect of the carbon source on UGA4 permease, ALA and GABA incorporation were measured in D27 strain, lacking GAP1 permease, and grown in proline as the sole nitrogen source, so the activity of PUT4 permease was negligible [15].

Analytical, diagnostic and therapeutic context of GAP1

• Gene disruption is effected by transforming a gap1 strain with a gene cassette generated by PCR, containing GAP1 flanked by short (60 bp) stretches of the gene in question [27].

References