Crystals of complexes mimicking protein biosynthesis are suitable for crystallographic studies

A complex of 70S ribosomes from Thermus thermophilus together with an average of 1.5–1.8 equivalents of $PhetRNA^{Phe}$ and a short mRNA chain, composed of 35 ± 5 uridines, was crystallized under the conditions used for the growth of crystals of isolated ribosomes from the same source. Considering the reproducibility of their growth, their internal order and their shape, the crystals of the complex are superior to those of isolated ribosomes. In accord with previous three-dimensional reconstruction and modeling experiments, we conclude that the complex is less flexible and that an average population of complexes is more homogeneous than that of isolated 70S ribosomes. The crystals of the complex diffract to higher than 15 Å resolution and can be irradiated with synchrotron X-ray beam at cryo-temperatures for days without noticeable decay. Since the crystals of the complex are apparently isomorphous with these of the isolated 70S ribosomes ($P4_12_12; a = b = 526; c = 315 Å)$, they should provide a tool for phasing as well as for locating the mRNA and tRNA binding sites