The Bacillus subtilis ochre suppressor sup-3 is located in an operon of seven tRNA genes

Most Bacillus subtilis tRNA genes have been isolated from lambda libraries by use of probes that hybridize to tRNA or rRNA sequences. None of those genes map to the region of the sup-3 mutation. By cloning of the sup-3 allele, a cluster of seven tRNA genes (the trnS operon) that had not been isolated by other methods was identified. In principle, this approach could be used to isolate at least one more predicted tRNA-containing operon in this bacterium. The trnS operon was shown to contain tRNA genes for Asn (GUU), Ser (GCU), Glu (UUC), Gln (UUG), Lys (UUU), Leu (UAG), and Leu (GAG). The sup-3 mutation was found to be a T-to-A transversion that changes the anticodon of the lysine tRNA from 5'-UUU-3' to 5'-UUA-3'. This result agrees with previous work that determined that the sup-3 mutation causes lysine to be inserted at ochre nonsense mutations.