Open Access5′-Terminal nucleotide sequence of Escherichia coli lactose repressor mRNA: Features of translational initiation and reinitiation sites
Author(s) -
Deborah A. Steege
Publication year - 1977
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.74.10.4163
Subject(s) - lac repressor , repressor , escherichia coli , nucleotide , messenger rna , sequence (biology) , terminal (telecommunication) , biology , nucleic acid sequence , genetics , chemistry , microbiology and biotechnology , gene , lac operon , gene expression , computer science , telecommunications
In a sequence of 214 nucleotides at the 5′ terminus of theI gene mRNA, which codes for the lactose repressor protein ofEscherichia coli , (i ) an untranslated leader sequence of 28 residues precedes the repressor coding region; (ii ) a GUG initiates synthesis of the wild-type repressor; (iii ) GUG and AUG are the functional initiators for the synthesis of restart polypeptides activated by earlyI gene amber mutations, confirming previous assignments for these residues based on protein sequencing data; and (iv ) sequences complementary to 16S ribosomal RNA provide stronger potential mRNA·16S rRNA interaction at the wild-type initiation site than at the restart sites. WhenI mRNA is used to direct the formation of initiation complexesin vitro , ribosomes bind only to the wild-type initiator region.A striking feature of theI mRNA sequence is the presence of a number of in-phase GUGs that have not been observed to serve as initiation signalsin vivo in the nonsense mutant strains examined. The selective use of potential initiator triplets in theI mRNA leads to the following conclusions. First, when presented with several neighboring initiator triplets at the wild-type initiator region, ribosomes select the one preceded by the strongest appropriately positioned complementarity to the 16S 3′ end. Second, ribosomes do not restart after termination simply by moving to the next available initiator codon. Third, the formation of stable secondary structures predicted for the untranslatedI mRNA beyond chain-terminating nonsense mutations may prevent ribosome access to some potential reinitiation sites.