1. Golden BL, Gooding AR, Podell ER, Cech TR. 1998. A preorganized active site in the crystal structure of the Tetrahymena ribozyme. Science 282:259-264 [Medline abstract]. Full-text HTML version
2. Cate, et al., 1996. Crystal Structure of a Group I Ribozyme Domain: Principles of RNA Packing. Science 273:1678. [Medline abstract] Full-text HTML version
The group I intron from Tetrahymena was the first RNA for which a catalytic activity was described (ribozyme). It consists of ~400 nts of RNA, shown below, which can self-splice itself from a ribosomal RNA transcript.
The crystal structure of most of the ribozyme has been determined.
(ref. 1) A domain of the intron, which has been shown to fold
autonomously, called P4-P5-P6, has also been crystallized (ref.
2). This tutorial covers part of both papers. The P4-P6 domain
is shown in purple, and the P3-P9 domain is shown in green. The
P3-P9 domain wraps around the P4-P6 domain.
Click here <
The crystal structure of the P4-P5-P6 domain of the group I
intron provided several novel discoveries. Besides being the largest
nucleic acid crystal structure solved to date, the structural
model provided information on the tetraloop receptor, the
tight turn, and the adenosine platform. You can
compare structures of these motifs in the crystal of the whole
ribozyme (this tutorial) with that for the P4-P6
domain alone. In general, the structure of the P4-P6 domain
is very similar in both structures.
Click here <
I. The tetraloop receptor
The GNRA tetraloop is a conserved 4 nucleotide loop which is commonly found on RNA helices. In a previous theoretical model of the groupI intron structure, Michel and Westoff noticed that the sequence of some GNRA tetraloops influenced the sequence of base pairs in other helices, suggesting that they might form a tertiary interaction. Costa and Michel further noticed that the GAAA tetraloop seemed to interact with a particular sequence motif, termed the tetraloop receptor. Click here to see the structure of the tetraloop and receptor <
II. The adenosine platform
Residues A225 and A226 within the tetraloop receptor form a structure termed the adenosine platform. These consecutive residues H-bond with each other (from N3 of A225 to N6 of A226) to form a motif which presents the adenosine residues for H-bonding or stacking with other residues. To zoom in on the adenosine platform of the tetraloop receptor, click here <
III. The tight turn
Residues 183 through 188 of the P4-6 domain form a tight turn of the RNA backbone. The phosphate oxygens of the backbone residues come within 3 angstroms in places. This is made possible by two Mg++ cations which coordinate with the phosphate oxygens of residues 183, 184, 186 and 187. Click here to zoom in on the tight turn <
IV. The ribose zipper
This region also includes another motif known as the ribose zipper, shown here <
This section Still Under Construction
Back to intro to RNA structure.