Functional analysis of multiple AUG codons in the transcripts of the STA2 glucoamylase gene from Saccharomyces cerevisiae

A scanning ribosome will usually initiate translation as soon as it encounters the first favourable AUG codon and only a few eukaryotic transcripts have more complex arrangements. These relatively few complex transcripts are normally characterized by structural features such as multiple AUGs and significant secondary structure. However, the functional relevance of these features has rarely been established. We present here a study of the functional significance of the multiple AUGs in the leader of STA2 transcripts of the budding yeast Saccharomyces cerevisiae, and extrapolate, where applicable, these results to a co-regulated gene, MUC1. The STA2 gene (a representative member of the polymorphic STA1-3 gene family), encodes an extracellular glucoamylase, and is evolutionarily linked to, and transcriptionally co-regulated with, the MUC1 gene, which encodes a mucin-like protein essential for pseudohyphal/invasive growth and cell-adhesion in S. cerevisiae. Each of these genes contains a putative upstream ORF, while STA2 has two additional in-frame AUG codons 5' to the major cistron. We show that utilization of the alternative translational start-sites of STA2 results in glucoamylases that differ at their N-termini, which are associated with differences in their localization patterns. Analysis of mutants revealed the presence of a putative secretion-enhancing signal that might prove to be relevant to the alternative targeting mechanism recently uncovered in S. cerevisiae. We show that a short upstream ORF present in the leaders of STA1-3 and MUC1 is probably bypassed by a process of leaky scanning.10 page(s

The S1, S2 and SGA1 ancestral genes for the STA glucoamylase genes all map to chromosome IX in Saccharomyces cerevisiae

The polymorphic extracellular glucoamylase-encoding genes STA1 (chr. IV), STA2 (chr. II) and STA3 (chr. XIV), from Saccharomyces cerevisiae var. diastaticus probably evolved by genomic rearrangement of DNA regions (S1, S2 and SGA1) present in S. cerevisiae, and subsequent translocation to unlinked regions of chromosomal regions. S1, encoding a homologue to the threonine/serine-rich domain of STA glucoamylases (GAI-III), mapped to the right arm of chromosome IX. S2, encoding the hydrophobic leader peptide of GAI-III, was also mapped on the right arm of chromosome IX, next to S1, close to DAL81. The SGA1 sporulation-specific, intracellular glucoamylase-encoding gene is located on the left arm of chromosome IX, 32 kb proximal of HIS5.Articl

A multicopy suppressor gene, MSS10, restores STA2 expression in Saccharomyces cerevisiae strains containing the STA10 represser gene

Transcription of the three unlinked, homologous STA1-3 glucoamylase-encoding genes, involved in starch degradation by Saccharomyces cerevisiae, was previously shown to be down-regulated by the presence of STA10, acting via three upstream repression sequence regions that were identified in the STA2 promoter. Here we report the cloning and characterization of a putative transcriptional activator gene, MSS10 (multicopy suppressor of STA10), which, when present in multiple copies, overcomes STA10 repression. Deletion of MSS10, located on chromosome XV, resulted in media-specific extinction of glucoamylase synthesis. The nucleotide sequence of MSS10 is identical to three other genes from S. cerevisiae identified as: FUP1, a gene that enhances iron-limited growth; PHD2, a gene identified for its ability to induce pseudohyphal growth in diploid cells grown on nitrogen-limited media; and MSN1, a gene encoding a transcriptional activator involved in invertase regulation.Articl