DESCRIPTION: The goal of this project is the determination of the structures of biologically relevant RNAs and ribonucleoprotein complexes by NMR. The data obtained will lead to better understanding of the mechanistic basis of the biological phenomena in which these RNAs participate, as well as contributing to the store of information about the conformational properties of RNAs in general. The RNAs whose structures will be studied first are: (1) pAD3 RNA, a derivative of the 5S rRNA from E. coli, which includes internal loop E, and binds to Ribrosomal protein L25, (2) the anticodon stem/loops from both an initiator and an elongator methionyl tRNA, the loops of which are identical in sequence but significantly different in conformation, and (3) the stem/loop IIa sequence from yeast U2 snRNA, which is believed to exist in two different conformations. Four other systems will also be pursued: mutational variants of sarcin/ricin stem/loop, stem/loop III from EBER 1, the kasugamycin stem/loop from the colicin fragment of the 16S rRNA of E. coil, and the bulge- helix-bulge motif from archael pre-rRNAs. The mutations whose conformational effects are to be examined in the sarcin/ricin system alter that RNA's activity as a substrate for either sarcin or ricin, but not both. EBER 1 is an RNA found in (mammalian) cells infected with Epstein-Barr virus. Its stem/loop IIa binds a ribosomal protein. The kasugamycin loop is normally heavily methylated; the objective is to understand the conformational effects of methylation. The archeal motif in question is a recognition signal for splicing, and its conformation may depend on interactions between its adjacent bulges.