Abstract
We describe a method to identify and analyze translationally regulative 5'UTRs (5'TRU) in Saccharomyces cerevisiae. Two-dimensional analyses of (35)S-methionine metabolically labeled cells revealed 13 genes and proteins, whose protein biosynthesis is post-transcriptionally up-regulated on amino acid starvation. The 5'UTRs of the respective mRNAs were further investigated. A plasmid-based reporter-testing system was developed to analyze their capability to influence translation dependent on amino acid availability. Most of the 13 candidate 5'UTRs are able to enhance translation independently of amino acids. Two 5'UTRs generally repressed translation, and the 5'UTRs of ENO1, FBA1, and TPI1 specifically up-regulated translation when cells were starved for amino acids. The TPI1-5'UTR exhibited the strongest effect in the testing system, which is consistent with elevated Tpi1p-levels in amino acid starved cells. Bioinformatical analyses support that an unstructured A-rich 5' leader is beneficial for efficient translation when amino acids are scarce. Accordingly, the TPI1-5'UTR was shown to contain an A-rich tract in proximity to the mRNA-initiation codon, required for its amino acid dependent regulatory function.