CRYSTAL-STRUCTURE OF AN RNA APTAMER PROTEIN COMPLEX AT 2.8 ANGSTROM RESOLUTION

The crystal structure, at 2.8 Angstrom resolution, of an RNA aptamer b ound to bacteriophage MS2 coat protein has been determined, It provide s an opportunity to compare the interactions of MS2 coat protein and w ild type operator with those of an aptamer, whose secondary structure differs from the wild type RNA in having a three-base loop (compared t o a tetraloop) and an additional base pair between this loop and the s equence-specific recognition element in the stem, The RNA binds in the same location on the coat protein as the wild type operator and maint ains many of the same RNA-protein interactions. In order to achieve th is, the RNA stem loop undergoes a concerted rearrangement of the 3' si de while leaving the 5' side and the loop interactions largely unchang ed, illustrating the ability of RNA to present similar molecular recog nition surfaces from distinct primary and secondary structures.