The 5'-flanking sequence of yeast tRNA(Leu3) genes enhances the rate of transcription from stable pre-initiation complexes.

A conserved sequence that enhances transcription is present at or near the 5'-end of genes which code for several abundant yeast tRNAs, one of which is tDNA(Leu3). Mutants with alterations in this region have been compared to the parent tDNA(Leu3) and a yeast tDNA(Ser) that normally lacks the conserved sequence. The apparent KM of the transcription apparatus is insensitive to 5'-flanking sequence variation. Replacement of the normal 5'-flanking sequence does result in 3-18 fold reductions in VMAX and a 7-13 fold loss of transcription in tests with competitor genes. A second template exclusion assay revealed that sequences upstream of the conserved region effect a 2 fold change in the ability of the genes to stably sequester a component(s) of the obligatory pre-initiation complex while positions -22 to +9 have little or no effect.