SOLUTION STRUCTURE OF THE CONSERVED 16S-LIKE RIBOSOMAL-RNA UGAA TETRALOOP

The solution structure of the highly conserved UGAA tetraloop found at the 3' end of eukaryotic 16 S-like ribosomal RNA has been solved by n uclear magnetic resonance spectroscopy in the form of the 12 nucleotid e hairpin 5'-GGUG[UGAA]CACC. The UGAA tetraloop displays a novel fold. The backbone turn occurs between the G and the third A in the loop, w ith the U and G in a 5' stack and the As in a 3' stacking arrangement. The loop is closed by a U-A mismatch in which the O2, 2'OH, and O4' g roups of the U are within hydrogen bonding distance of the amino group of the A. The tetraloop does riot make a uridine-turn, even though it s sequence is identical to a U-turn found within the anticodon loop of tRNA(Phe). The hydrogen bonding pattern in the tetraloop provides ins ight into the function of base modifications found in vivo within this portion of 16 S-like rRNA. (C) 1997 Academic Press Limited.