| Abstrakt: |
The BAP3 gene of Saccharomyces cerevisiae encodes a protein with a high similarity to the BAP2 gene product, a high-affinity permease for branched-chain amino acids. In this paper, we show that, like BAP2 , the expression of the BAP3 gene in S. cerevisiae is induced by the addition of branched-chain amino acids to the medium. Unexpectedly, most other naturally occurring L-amino acids found in proteins (with the exception of proline, lysine, arginine and histidine) have the same effect on the expression of BAP3 . The induction of BAP3 expression appears to be dependent on Stp1p, a nuclear protein, previously shown to be involved in pre-tRNA maturation and also required for the expression of BAP2 , as induction is no longer observed in an stp1 - mutant. The transcriptional regulator Leu3p is not involved in the induction of BAP3 expression, but may act as a repressor of BAP3 expression in the absence of leucine, as can be inferred from a transcriptional analysis in a Δleu3 mutant. By extensive deletion analysis of the BAP3 promoter fused to a GUS reporter, as well as by fusions of different parts of the BAP3 promoter to a LacZ reporter, we have found that a portion of the BAP3 promoter from - 418 to - 392 relative to the ATG start codon is both necessary and sufficient for the Stp1p-dependent induction of BAP3 expression by (most) amino acids. We have therefore named this sequence UASaa (amino acid-dependent upstream activator sequence). Neither Stp1p nor Leu3p appear to bind to the UASaa , at least in vitro , as judged from gel retardation assays. Sequences similar to the UASaa can be found in the promoters of BAP2, PTR2 and TAT1 ; genes that, like BAP3 , encode permeases inducible by amino acids, suggesting that amino acid induction of all these genes is exerted via a common mechanism. [ABSTRACT FROM AUTHOR] |
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