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Figure 4.
Figure 4 Structural components of the active site. a,
Solvent-accessible surface of the ribozyme-U1A-RBD complex,
orientated as in Fig. 3a, colour-coded by its curvature (green,
convex; grey, concave^49). The atoms of the ribose ring of G1
are shown as red spheres; the 5'-hydroxyl group points away from
the reader into the ribozyme. The trajectory proposed to be
followed by nucleotides located 5' of the cleavage site in the
precursor is indicated by the row of small red dots. b, The
substrate-bearing nucleotide G1 forms a wobble pair with U37
which stacks on P1.1. The 5'-hydroxyl group (shown as a larger
sphere) is within hydrogen-bonding distance of the Watson-Crick
face of C75. Nucleotides are coloured as in Figs 2 and 3.
Phosphorus atoms are coloured green. Oxygen and nitrogen atoms
that participate in noteworthy hydrogen bonding (denoted by
two-headed arrows) are coloured red and blue, respectively. c,
Triple-strand junction between P3 and P1, orientated as in Fig.
3a. A hydrogen bond between the N1 group of A78 and the O2'
group of G29 is obscured in this view.
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