Dimeric tRNA precursors in yeast

Abstract

Two DNA fragments, each containing a tRNA₃^Arg and a tRNA^Asp gene in close conjunction, have been isolated from different genomic regions of Saccharomyces cerevisiae¹. Nucleotide sequence analysis of the gene regions revealed that in both fragments the tRNA₃^Arg coding region is located 5′-proximal to the tRNA^Asp coding region. They are separated by an identical spacer of 10 nucleotides. Although the 5′-flanking sequences are different in the two plasmids, some similarities are observed. To test the mode of expression of this gene configuration, we transcribed the DNA fragments in a Xenopus oocyte nuclear extract^2,3. Specific transcription of the yeast tRNA genes took place in an RNA precursor which comprised both tRNA species. We report here that the precursor RNA was processed to the mature-sized tRNA molecules, indicating the presence of an enzyme activity in the Xenopus nucleus capable of cutting a dimeric tRNA precursor. This is the first observation of a eukaryotic dimeric tRNA precursor.