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  • 1
    ISSN: 1432-0983
    Keywords: Key wordsSaccharomyces cerevisiae  ;  Amino-acid uptake  ;  STP1  ;  BAP2  ;  GCN4
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The bap1 mutant of Saccharomyces cerevisiae was previously isolated by its reduced uptake of branched-chain amino acids. In the present study, the corresponding wild-type gene was cloned and partial sequencing and subsequent genetic analysis revealed identity to STP1, a gene involved in tRNA maturation. The decrease in amino-acid uptake caused by stp1 mutations is independent of GCN4. It was previously found that the BAP2 promoter can be activated by the presence of amino acids, notably leucine, in the medium. We found that this activation depends on STP1. As a simple hypothesis we propose that Stp1p is a transcription factor which activates BAP2, and probably other amino-acid permease genes.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0983
    Keywords: Key words Cysteine uptake ; Amino-acid permeases ; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 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. Overexpression studies identified BAP2, BAP3, AGP1 and GNP1 as genes encoding transporters of cysteine. Uptake studies with disruption mutants confirmed this, and identified two additional genes for transporters of cysteine, TAT1 and TAT2, both very homologous to BAP2, BAP3, AGP1 and GNP1. While Gap1p and Agp1p appear to be the main cysteine transporters on the non-repressing nitrogen source proline, Bap2p, Bap3p, Tat1p, Tat2p, Agp1p and Gnp1p are all important for cysteine uptake on ammonium-based medium. Furthermore, whereas Bap2p, Bap3p, Tat1p and Tat2p seem most important under amino acid-rich conditions, Agp1p contributes significantly when only ammonium is present, and Gnp1p only contributes under the latter condition.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 7 (1991), S. 933-941 
    ISSN: 0749-503X
    Keywords: BAP1 ; branched-chain amino acids ; transport ; permease ; uptake ; L-isoleucine ; L-leucine ; L-valine ; sulfometuron methyl ; yeast ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: In order to isolate mutants with impaired uptake of branched-chain amino acids, mutants were induced which on complex medium were sensitive to an inhibitor of branched-chain amino acid biosynthesis. Eighteen mutants of independent origin were found. Ten of them were assayed for branched-chain amino acid uptake. Three of these were impaired in the uptake of L-valine, L-isoleucine and L-leucine, while the rest were unaffected in uptake of any of the three amino acids. Kinetics of the uptake by one selected mutant and the parental strain S288C were compared to models for one or two systems obeying Michaelis-Menten kinetics. This analysis suggested that a high-affinity system for all three amino acids is absent in the mutant, whereas low-affinity uptake of L-isoleucine and L-leucine by one or more systems remains unaffected. Moreover, medium-affinity uptake components for L-valine and L-leucine, not originally seen in the wild type, were identified in the mutant. In the wild type, 10 mM of any of the amino acids L-alanine, L-cysteine, L-isoleucine, L-leucine, L-tryptophan and L-valine reduce uptake of any of the three branched-chain amino acids. We propose that a permease responsible for high-affinity uptake of the branched-chain amino acids in strain S288C is partially or completely inactive in the mutant. Tetrad analysis shows that the phenotype can be ascribed to a single Mendelian gene. The wild-type allele is denoted BAP1 for branched-chain amino acid permease. The BAP1-dependent system is different from the general amino acid permease.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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