title: Evidence for regulation of reinitiation in translational control of GCN4 mRNA.
abstract: Translational control of the GCN4 gene of Saccharomyces cerevisiae is mediated by four upstream open reading frames (URFs) present in the leader of GCN4 mRNA. URFs 3 and 4 efficiently repress GCN4 expression in normal growth conditions; URFs 1 and 2 are required to overcome this repression in amino acid-starved cells. lacZ fusions to URFs 3 and 4 were used to determine the translational event that is regulated at these sequences by URFs 1 and 2. URF3-lacZ, URF4-lacZ, and GCN4-lacZ fusions are affected similarly by URFs 1 and 2 when no other URFs are present in the leader: expression from all three fusions is reduced by an amount slightly greater in repressing than in derepressing conditions. These results are inconsistent with models that postulate a differential effect of URFs 1 and 2 on initiation or elongation rates at URFs 3 and 4 versus the GCN4 coding sequences. We propose that the efficiency of reinitiation at the GCN4 AUG codon after translation of URFs 3 and 4 is the translational event that is stimulated in derepressing conditions by URFs 1 and 2.
mesh_terms: D001483:Base Sequence; D003001:Cloning, Molecular; D003062:Codon; D008969:Molecular Sequence Data; D010957:Plasmids; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics*
chemical_list: D003062:Codon; D012333:RNA, Messenger