Short peptide coding regions (upstream open reading frames or uORFs) in the 5'-leaders of eukaryotic mRNAs can serve critical regulatory functions. uORFs are found in many mR_NAs in filamentous fungi. A single uORF with an evolutionarily conserved peptide sequence is found upstream of the structural genes for the small subunit of arginine-specific carbamoyl phosphate synthetase from Neurospora crassa, Magnaporthe grisea, Trichoderma virens, Aspergillus nidulans and Saccharomyces cerevisiae. The N. crassa uORF specifies a 24-residue peptide named the arginine attenuator peptide (AAP) because it is involved in negative, Arg-specific translational regulation. In vivo, the N. crassa AAP down-regulates translation of ARG2 in response to Arg by reducing the average number of ribosomes associated with the arg-2 mRNA. AAP-mediated translational regulation has been reconstituted in an N. crassa cell-free translation system. A primer extension inhibition assay has been used to map the positions of ribosomes on capped and polyadenylated synthetic RNAs added to this system. Arg causes ribosomes to stall soon after they have translated the AAP. Arg-specific ribosome stalling is proposed to result in Arg-specific negative regulation because such ribosomes would block ribosomal scanning from the 5'-end of the mRNA and therefore block trailing ribosomes from translating ARG2. The AAP amino acid sequence, but not the RNA sequence encoding it, is critical for regulation. AAP translation can cause stalling of ribosomes involved in termination or elongation. Regulation by these evolutionarily conserved fungal leader peptides represent a novel mechanism of cis-acting translational control.
Fungal Genet. Newsl. 46 (Supl):
Full conference title:
Fungal Genetics Conference 20th
- Fungal Genetics Conference 20th (1999)