In vitro transcription of three adjacent E. coli transfer RNA genes

Abstract

RECENT evidence suggests that the structural genes of some transfer RNA molecules are clustered in groups of two or three on the Escherichia coli chromosome^1–5. The arrangement of tRNA and spacer sequences for two such tRNA clusters have been described^6–8. The pattern of transcription of tRNA genes in clusters is not known although the formation of larger precursors in tRNA biosynthesis has been reported^9,10. In vitro transcription of tRNA₁^Tyr gene carried by ϕ80psu₃⁺ phage DNA by purified RNA polymerase was shown to result in the formation of pre-tRNA^Tyr molecules bigger in size than mature tRNA¹¹. In the present communication we describe the transcription of a tRNA gene cluster (tRNA₂^Gly(su⁺₃₆), tRNA₂^Tyr, tRNA₃^Thr) carried by the DNA of transducing phage λh80cI857S⁻t68dglyTsu⁺₃₆tyrTthrT (abbreviated λh80T) recently isolated by Squires et al.⁵. In vitro transcription of this phage DNA by purified RNA polymerase is shown to produce pre-tRNA molecules of a molecular size consistent with the model of a polycistronic precursor.