The transcriptional efficiency of clustered tRNA genes is affected by their position within the cluster

The transcription of a mouse genomic segment containing four tRNA genes, coding for a tRNA(Ala), a tRNA(Ile), a tRNA(Pro) and a tRNA(Lys), has been studied in a HeLa cell extract, demonstrating that differences among their transcriptional efficiencies are evident using as templates either the natural cluster or an equimolecular mixture of the four isolated genes. Nevertheless, the structure of the cluster influences the transcriptional efficiency of the clustered genes. In fact, a cis-acting inhibitory sequence has been located at about 400 bp downstream of the tRNA(Pro) coding sequence. Moreover rearrangements of the reciprocal position of the various tRNA genes within the cluster results in significant changes in the transcriptional rates of the individual transcriptional units.