CRYSTAL-STRUCTURE OF 2'-O-ME(CGCGCG)(2), AN RNA DUPLEX AT 1.30 ANGSTROM RESOLUTION - HYDRATION PATTERN OF 2'-O-METHYLATED RNA

The molecular and crystal structure of 2'-O-Me (CGCGCG)(2) has been de termined using synchrotron radiation at near-atomic resolution (1.30 A ngstrom), the highest resolution to date in the RNA field. The crystal structure is a half-turn A-type helix with some helical parameters de viating from canonical A-RNA, such as low base pair rise, elevated hel ical twist and inclination angles. In CG steps, inter-strand guanines are parallel while cytosines are not parallel. In steps GC this motif is reversed. This type of regularity is not seen in other RNA crystal structures. The structure includes 44 water molecules and two hydrated Mg2+ ions one of which lies exactly on the crystallographic 2-fold ax is. There are distinct patterns of hydration in the major and the mino r grooves. The major groove is stabilised by water clusters consisting of fused five- and six-membered rings. Minor groove contains only a s ingle row of water molecules; each water bridges either two self-paral lel cytosines or two self-parallel guanines by a pair of hydrogen bond s. The structure provides the first view of the hydration scheme of 2' -O-methylated RNA duplex.