Protein Synthesis in Archaea

We are also studying protein synthesis in archaea. The archaeal protein synthesis machinery is a mosaic with some features found in eubacteria and others found in eukaryotes. Mutant initiator tRNAs and protein coding genes carrying mutations in the initiation codon are being used to study the requirements in an archaeal initiator tRNA for its function. We have shown that, in the presence of a mutant initiator tRNA that can read the GUC codon, GUC can be used as an initiation codon in halobacteria.

We are also interested in understanding the mechanism by which an archaeal isoleucine tRNA reads the rare isoleucine codon AUA without also reading AUG, the codon for methionine. In eubacterial isoleucine tRNA, the modified base lysidine derived from cytidine, is used to exclusively base pair with A. In eukaryotic isoleucine tRNAs, modified bases pseudouridine and inosine – each found in one of the two isoleucine tRNAs – can base pair with A without base pairing with G. We have recently found that the archaeal isoleucine tRNA, which reads AUA, also has a modified base derived from cytidine, but it is not lysidine, pseudouridine, or inosine. Current work is aimed at identification of the modified base and enzymes involved in its biosynthesis.