Molecular and Cellular Biology, December 1998, p. 7528-7536, Vol. 18, No. 12
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Department of Biochemistry and Molecular Biology, Oregon Graduate Institute of Science & Technology, Portland, Oregon 97291-1000,1 and Department of Molecular Microbiology and Immunology, Oregon Health Sciences University, Portland, Oregon 97201-30982
Received 17 July 1998/Returned for modification 21 August 1998/Accepted 28 August 1998
Translation of the upstream open reading frame (uORF) in the 5' leader segment of the Neurospora crassa arg-2 mRNA causes reduced initiation at a downstream start codon when arginine is plentiful. Previous examination of this translational attenuation mechanism using a primer-extension inhibition (toeprint) assay in a homologous N. crassa cell-free translation system showed that arginine causes ribosomes to stall at the uORF termination codon. This stalling apparently regulates translation by preventing trailing scanning ribosomes from reaching the downstream start codon. Here we provide evidence that neither the distance between the uORF stop codon and the downstream initiation codon nor the nature of the stop codon used to terminate translation of the uORF-encoded arginine attenuator peptide (AAP) is important for regulation. Furthermore, translation of the AAP coding region regulates synthesis of the firefly luciferase polypeptide when it is fused directly at the N terminus of that polypeptide. In this case, the elongating ribosome stalls in response to Arg soon after it translates the AAP coding region. Regulation by this eukaryotic leader peptide thus appears to be exerted through a novel mechanism of cis-acting translational control.
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