Table 1.

Prevalence of the indirect and direct pathways for the synthesis of the aa-tRNA species listed in all three domains of life

aa-tRNA	Prevalence of		Refs.
	Indirect pathway	Direct pathway
Gln-tRNAGln	All known archaea, most bacteria, and chloroplasts	All known eukaryotes and a minority of bacteria	3, 4, 17, 18
Asn-tRNAAsn	Most bacteria and archaea	All known eukaryotes and a number of bacteria and archaea	3–5, 38
Cys-tRNACys	Methanogenic archaea (except M. smithii and M. stadtmanae) and A. fulgidus	All known eukaryotes and bacteria, and most archaea	6–8, 11, 77, 80–82
Sec-tRNASec	All known Sec-decoding eukaryotes, archaea and bacteria	None known	107–110, 118