HAMMERHEAD RIBOZYME - A 3-DIMENSIONAL MODEL-BASED ON PHOTO-CROSS-LINKING DATA

The hammerhead ribozyme is a small catalytic RNA motif made up of 3 ba se-paired stems connected by conserved sequences which are essential f or catalysis. We have modelled its 3 dimensional structure, taking adv antage of proximity data between several substrate and ribozyme residu es determined by photo-crosslinking experiments. It is characterized b y an Y shape of the 3 stems stabilized in the central core by a networ k of hydrogen bonds involving in particular 2 non Watson-Crick G:A bas e-pairs. The 5' conserved sequence CUGA makes a sharp turn, the G resi due exchanging hydrogen bonds with a conserved base-pair of stem III. The substrate is stretched at the cleavage site. Overall this structur e is consistent with that deduced from X-ray crystallography but diffe rences are observed at the level of the CUGA turn.