Suppression of Amber Codons in Caulobacter crescentus by the Orthogonal Escherichia coli Histidyl-tRNA Synthetase/tRNA(His) Pair

While translational read-through of stop codons by suppressor tRNAs is common in many bacteria, archaea and eukaryotes, this phenomenon has not yet been observed in the α-proteobacterium Caulobacter crescentus. Based on a previous report that C. crescentus and Escherichia coli tRNA(His) have distinctive identity elements, we constructed E. coli tRNA(His) (CUA), a UAG suppressor tRNA for C. crescentus. By examining the expression of three UAG codon- containing reporter genes (encoding a β-lactamase, the fluorescent mCherry protein, or the C. crescentus xylonate dehydratase), we demonstrated that the E. coli histidyl-tRNA synthetase/tRNA(His) (CUA) pair enables in vivo UAG suppression in C. crescentus. E. coli histidyl-tRNA synthetase (HisRS) or tRNA(His) (CUA) alone did not achieve suppression; this indicates that the E. coli HisRS/tRNA(His) (CUA) pair is orthogonal in C. crescentus. These results illustrate that UAG suppression can be achieved in C. crescentus with an orthogonal aminoacyl-tRNA synthetase/suppressor tRNA pair.