4ULX:
reference: Mutational studies on resurrected ancestral proteins reveal conservation of site-specific amino acid preferences throughout evolutionary history., Risso VA, Manssour-Triedo F, Delgado-Delgado A, Arco R, Barroso-delJesus A, Ingles-Prieto A, Godoy-Ruiz R, Gavira JA, Gaucher EA, Ibarra-Molero B, Sanchez-Ruiz JM, Mol Biol Evol. 2014 Nov 12. pii: msu312. PMID: 25392342

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