A number of evolutionary scenarios have been proposed for the pyrrolysine system. The current (2022) view, given available sequences for tRNA and Pyl-tRNA (PylRS) synthase genes, is that: tRNA(Pyl) diverged from tRNA(Phe) some time between the divergence of the three domains (~LUCA) and the divergence of archaeal phyla, but was lost in non-archaeal lineages; PylRS originated within a common ancestor of all archaea. A number of domain organizations of PylRS is known: pylS itself consists of an N-terminal tRNA-binding domain and a C-terminal synthase domain, but other organizations consist of two domains in separate proteins or a protein made up of a lone C-terminal domain. The CTD probably originated from PheRS. The NTD is an archaeal innovation with no known relative. The ancestral PylRS probably adopted the "two separate proteins" configuration. The "genetic code expansion cassette" was later transferred into various bacteria. This cassette's PylRS has a split-domain configuration.
a number of evolutionary scenarios have been proposed for the pyrrolysine system the current (2022) view given available sequences for trna and pyl-trna (pylrs) synthase genes is that trna(pyl) diverged from trna(phe) some time between the divergence of the three domains (~luca) and the divergence of archaeal phyla but was lost in non-archaeal lineages; pylrs originated within a common ancestor of all archaea a number of domain organizations of pylrs is known pyls itself consists of an n-terminal trna-binding domain and a c-terminal synthase domain but other organizations consist of two domains in separate proteins or a protein made up of a lone c-terminal domain the ctd probably originated from phers the ntd is an archaeal innovation with no known relative the ancestral pylrs probably adopted the "two separate proteins" configuration the "genetic code expansion cassette" was later transferred into various bacteria this cassette's pylrs has a split-domain configuration