NATIVE 3D STRUCTURE OF EUKARYOTIC 80S RIBOSOME - MORPHOLOGICAL HOMOLOGY WITH THE ESCHERICHIA-COLI 70S RIBOSOME

A three-dimensional reconstruction of the eukaryotic 80S monosome from a frozen-hydrated electron microscopic preparation reveals the native structure of this macromolecular complex. The new structure, at 38 An gstrom resolution, shows a marked resemblance to the structure determi ned for the E. coli 70S ribosome (Frank, J., A. Verschoor, Y. Li, J. Z hu, R.K. Lata, M. Radermacher, P. Penczek, R. Grassucci, R.K. Agrawal, and S. Srivastava. 1996b. In press; Frank, J., J. Zhu, P. Penczek, Y. Li, S. Srivastava, A. Verschoor, M. Radermacher, R. Grassucci, R.K. L ata, and R. Agrawal. 1995. Nature (Lond.). 376:441-444.) limited to a comparable resolution, but with a number of eukaryotic elaborations su perimposed. Although considerably greater size and intricacy of the fe atures is seen in the morphology of the large subunit (60S vs 50S), th e most striking differences are in the small-subunit morphology (40S v s 30S): the extended beak and crest features of the head, the back lob es, and the feet. However, the structure underlying these extra featur es appears to be remarkably similar in form to the 30S portion of the 70S structure. The intersubunit space also appears to be strongly cons erved, as might be expected from the degree of functional conservation of the ribosome among kingdoms (Eukarya, Eubacteria, and Archaea). Th e internal organization of the 80S structure appears as an armature or core of high-density material for each subunit, with the two cores li nked by a single bridge between the platform region of the 40S subunit and the region below the presumed peptidyltransferase center of the 6 0S subunit. This may be equated with a close contact of the 18S and 28 S rRNAs in the translational domain centered on the upper subunit:subu nit interface.