Nucleotide Sequences at the Two Ends of the E. coli Tyrosine tRNA Genes and Studies on the Promoter

Abstract

INTRODUCTION
Escherichia coli contains two species of tyrosine tRNA, tRNA₁^Tyr and tRNA₂^Tyr (Nishimura et al. 1967; Goodman et al. 1968). The minor species (tRNA₁^Tyr) is specified by a gene that has undergone tandem duplication and that maps at 26 minutes on the chromosome (Russell et al. 1970). One of the tandem genes can mutate to give a suppressor gene, Su_III⁺. By transduction, these tandem genes can be integrated into the bacteriophage φ80 to give the strain φ80psu_III⁺⁻ (doublet) (Smith et al. 1967). Unequal recombination between the adjacent genes gives rise to a single-gene (singlet) strain, φ80psu_III⁺, (Russell et al. 1970).

A precursor to tRNAsuIII+Tyr isolated from E. coli cells infected by the singlet strain has been sequenced (Altman and Smith 1971). The presence of the pppG nucleotide at the 5′ end of the sequence indicates that the precursor contains the initiation point for gene transcription by E. coli RNA polymerase.

The gene for the major species, tRNA₂^Tyr, maps at 79 minutes on the E. coli chromosome and it also can be integrated into the transducing phage λh80dglyT Su₃₆⁺ together with genes for tRNA₂^Gly and tRNA₃^Thr, all three genes forming a cluster (Squires et al. 1973).

In an approach to determining the nucleotide sequences beyond the C-C-A end and into the promoter region, suitable synthetic deoxyribo-polynucleotides (primers) were hybridized to the appropriate separated strands of the singlet strain φ80psu_III⁺ DNA and controlled elongation was effected by E. coli DNA polymerase I. In this way, the 23-nucleotide sequence beyond the C-C-A end...