title: The evolution of Class II Aminoacyl-tRNA synthetases and the first code.
abstract: Class II Aminoacyl-tRNA synthetases are a set of very ancient multi domain proteins. The evolution of the catalytic domain of Class II synthetases can be reconstructed from three peptidyl-hairpins. Further evolution from this primordial catalytic core leads to a split of the Class II synthetases into two divisions potentially associated with the operational code. The earliest form of this code likely coded predominantly Glycine (Gly), Proline (Pro), Alanine (Ala) and "Lysine"/Aspartic acid (Lys/Asp). There is a paradox in these synthetases beginning with a hairpin structure before the Genetic Code existed. A resolution is found in the suggestion that the primordial Aminoacyl synthetases formed in a transition from a Thioester world to a Phosphate ester world.
authors.affiliation: BioMedical Engineering, Boston University, Boston, MA 02215, USA. Electronic address: templesmith1@comcast.net.
authors.forename: Temple F
authors.initials: TF
authors.lastname: Smith
authors.affiliation: Earth, Atmosphere, and Planetary Science Department, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Electronic address: hhartman@mit.edu.
authors.forename: Hyman
authors.initials: H
authors.lastname: Hartman
mesh_terms: D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry / Q000378:metabolism*; D020134:Catalytic Domain; D019143:Evolution, Molecular; D008958:Models, Molecular
chemical_list: D000604:Amino Acyl-tRNA Synthetases
keywords: Aminoacyl-tRNA-synthetase; Evolution; Operational-code; Thioester