Transcription of multimeric tRNA genes.

We have constructed a set of plasmids carrying a tRNAPro gene from C. elegans in a head to tail dimeric and trimeric arrangement with virtually no spacer sequence. We show that in two different transcriptional systems, each coding region functions as an internal promoter directing the synthesis of independent transcriptional products. This is in contrast with the property of natural head to tail dimeric arrangements found in yeast, where only one coding region functions as promoter (Mao et al., 1980 Cell 20, 589; Schmidt et al., 1980 Nature 287, 750). The evolutionary significance of our finding is discussed.