Escherichia coli tRNATyr Gene Clusters: Organization and Structure

Abstract

Escherichia coli contains two species of tRNA^Tyr that differ from each other by only two bases in the variable loop region (Goodman et al. 1968Goodman et al. 1970). The locus tyrT at 27 minutes (Garen et al. 1965; Signer et al. 1965; Bachman et al. 1976) has been shown to contain duplicate copies of the tRNA₁^Tyr sequence, since the bacteriophage φ80psu⁺⁻3 stimulates the production of both su⁺ and su⁻ tRNA₁^Tyr (Russell et al. 1970). Derivatives of this bacteriophage, carrying only a single su⁺ tRNA₁^Tyr copy, have been isolated. These are presumed to arise by unequal recombination involving the two tRNA₁^Tyr mature structural sequences (Russell et al. 1970). The tyrU locus, on the opposite side of the E. coli chromosome at 88 minutes (Orias et al. 1972), codes for tRNA₂^Tyr (Eggerston and Adelberg 1965; Orias et al. 1972; Squires et al. 1973) and has been shown to contain a single tRNA₂^Tyr mature structural sequence.

We are attempting to determine those aspects of tRNA gene structure and organization that are crucial to the initiation and termination of transcription and the regulation of gene expression. The tRNA^Tyr genes of E. coli, which have already figured prominently in this area, afford a model system well suited for studying this group of problems. In the experiments described here, the tRNA₁^Tyr transducing phages φ80psu⁺⁻3 (doublet) and φ80psu⁺3 (singlet) (Russell et al. 1970), and the tRNA₂^Tyr transducing phages λh80dglyTsu⁺36 (Squires et al. 1973) and λrif^d18 (Kirschbaum and Konrad 1973) have been used to study the structural organizations of regulatory...