RIBOZYME CATALYSIS FROM THE MAJOR GROOVE OF GROUP-II INTRON DOMAIN-5

The most highly conserved nucleotides in D5, an essential active site component of group II introns, consist of an AGC triad, of which the G is invariant. To understand how this G participates in catalysis, the mechanistic contribution of its functional groups was examined. We ob served that the exocyclic amine of G participates in ground state inte ractions that stabilize D5 binding from the minor groove. In contrast, each major groove heteroatom of the critical G (specifically N7 or O6 ) is essential for chemistry. Thus, major groove atoms in an RNA helix can participate in catalysis, despite their presumed inaccessibility. N7 or O6 of the critical G could engage in critical tertiary interact ions with the rest of the intron or they could, together with phosphat e oxygens, serve as a binding site for catalytic metal ions.