HAMMERHEAD RIBOZYMES WITH A FASTER CLEAVAGE RATE

A hammerhead ribozyme that was previously reported to have a rate of c hemical cleavage 10-fold faster than that of conventional hammerheads was analyzed in greater detail. Although originally found as a bimolec ular hammerhead assembled through helices I and II, fast cleavage was observed in hammerheads in the more conventional helix I-helix III for m, provided the sequence of helix I of the fast hammerhead was preserv ed. Mutations indicated that the fast rate of cleavage was due to the presence of both the U1.1-A2.1 and A1.2-U2.2 base pairs. The faster ra te of cleavage was due to a small increase in the activation entropy o f the reaction. In addition, we confirmed previous reports that increa sing the length of helix I by greater than five base pairs inhibits cl eavage slightly and have uncovered a similar effect in helix II.