The first protein in the large subunit has been given the designation L1. This protein is composed of two domains, which are extremely important in binding of rRNA. At the end of the N-terminal region in the first domain lies a group of eight flexible residues, which are directly involved in the binding of the 23S rRNA. These amino acid residues are located at the space between the two domain regions, which allows for the RNA to enter and bind. The structure shown above was isolated from the archae Thermus thermophilus and determined via X-ray crystallography. Proposed mechanims of binding have included the induced fit model, and L1 appears to have a secondary role as a repressor of mRNA. (Tishchenko et al. 1996)