University of Illinois researchers report the dual functions of transfer RNA, or tRNA -- a molecule that delivers amino acids to the protein-building machinery of the cell -- apparently originated independently.

"Structure is highly conserved, capturing information that is evolutionarily deep," said Professor Gustavo Caetano-Anolles, who led the study. "It was only logical to focus on transfer RNA, a molecule that is believed to be very ancient and is truly central to the entire protein synthesis machinery."

During protein synthesis, tRNA's dual function is reflected in its unique L-shaped structure, the scientists said. One end of the molecule decodes messenger RNA -- a molecule that carries instructions for the sequence of amino acids in a protein -- while the other transfers a specific amino acid to the growing protein chain.

Previously scientists assumed the two functional domains of tRNA had evolved together. But Caetano-Anolles and researcher Feng-Jie Sun determined the two functions have different evolutionary histories, which suggests they were acquired at different points in time.

The research appeared in the July 30 issue of the online journal PLoS One.