gene is composed of three

The 71-base-pair coding sequence of the tRNAPro gene from Caenorhabditis elegans contains all of the information required for transcription and processing in the injected oocytes. Several subclones of the DNA coding for the tRNAr? were con- structed, carrying deletions or insertions, or both. Their tran- scriptional properties lead to the hypothesis that the tRNAPr? gene promoter is composed of three discontinuous regions within the coding sequence. In previous studies we have characterized steps in the synthesis of mature tRNA molecules in eukaryotic cells by injecting cloned DNAs coding for tRNA into Xenopus laevis oocytes (1-4). These studies have shown that tRNA genes are tran- scribed into precursor molecules, which are converted into tRNAs through a series of nucleolytic cleavages and nucleotide modifications. In order to gain further insight into the process of tRNA bio- synthesis and to determine how cells regulate the expression of these genes, it will be instructive to identify the transcrip- tional signals present on the DNA sequence and recognized by the RNA polymerase III. The work of Brown and his colleagues (5, 6) has revealed that the relatively small 5S RNA gene con- tains a 30-base-pair region within the coding sequence that is essential for initiation of transcription by RNA polymerase III. Also for tRNA genes (7-10), it appears probable that their pro- moters are not located in the 5' flanking region, even though this region may play a regulatory role in some cases (9, 10). It is unclear, however, whether they have an internal control re- gion analogous to that of the 5S RNA genes. To establish this, we constructed deletion and insertion mutants, altering se- quences within the coding regions of the tRNAPr? gene of Cae- norhabditis elegans. This allowed the identification of three sep- arated regions within the coding sequence that are important