title: Translation initiation: a regulatory role for poly(A) tracts in front of the AUG codon in Saccharomyces cerevisiae.
abstract: The 5'-UTR serves as the loading dock for ribosomes during translation initiation and is the key site for translation regulation. Many genes in the yeast Saccharomyces cerevisiae contain poly(A) tracts in their 5'-UTRs. We studied these pre-AUG poly(A) tracts in a set of 3274 recently identified 5'-UTRs in the yeast to characterize their effect on in vivo protein abundance, ribosomal density, and protein synthesis rate in the yeast. The protein abundance and the protein synthesis rate increase with the length of the poly(A), but exhibit a dramatic decrease when the poly(A) length is ≥12. The ribosomal density also reaches the lowest level when the poly(A) length is ≥12. This supports the hypothesis that a pre-AUG poly(A) tract can bind to translation initiation factors to enhance translation initiation, but a long (≥12) pre-AUG poly(A) tract will bind to Pab1p, whose binding size is 12 consecutive A residues in yeast, resulting in repression of translation. The hypothesis explains why a long pre-AUG poly(A) leads to more efficient translation initiation than a short one when PABP is absent, and why pre-AUG poly(A) is short in the early genes but long in the late genes of vaccinia virus.
authors.affiliation: Department of Biology, University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada. xxia@uottawa.ca
authors.forename: Xuhua
authors.initials: X
authors.lastname: Xia
authors.forename: Vivian
authors.initials: V
authors.lastname: MacKay
authors.forename: Xiaoquan
authors.initials: X
authors.lastname: Yao
authors.forename: Jianhua
authors.initials: J
authors.lastname: Wu
authors.forename: Fumihito
authors.initials: F
authors.lastname: Miura
authors.forename: Takashi
authors.initials: T
authors.lastname: Ito
authors.forename: David R
authors.initials: DR
authors.lastname: Morris
mesh_terms: D020121:5' Untranslated Regions / Q000235:genetics; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D003062:Codon / Q000235:genetics*; D010448:Peptide Initiation Factors / Q000235:genetics / Q000378:metabolism; D011061:Poly A / Q000235:genetics* / Q000378:metabolism; D039102:Poly(A)-Binding Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D014176:Protein Biosynthesis / Q000235:genetics*; D012270:Ribosomes / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D020121:5' Untranslated Regions; D003062:Codon; D010448:Peptide Initiation Factors; D039102:Poly(A)-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; C450100:pab1 protein, S cerevisiae; D011061:Poly A