“…Transfer RNA was the first, and is at present the only, nucleic acid to form single crystals large enough for an X-ray diffraction study. The flurry of activity that ensued in the nine years following the first crystallization (Cramer et al 1968;Fresco, Blake & Langridge, 1968;Clark et al 1968;Hampel et al 1968;Kim & Rich, 1968) has resulted in the production of four sets of atomic co-ordinates (Sussman & Kim, 1976 a;Stout et al 1976;Quigley et al 1975;Ladner et al 1975) all for yeast phenylalanine tRNA. Several reviews have been written which trace both the history and the electron density maps of tRNA (Rich & Raj-Bhandary, 1976;Kim, 1976Kim, , 1977Sussman & Kim, 1976&;Arnott, 1971;Sigler, 1975).…”