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 the entire ribozyme has not been determined.
However, a domain of the intron, which has been shown to fold
autonomously, called P4-P5-P6, has been crystallized.
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 <
This section Still Under Construction