Conserved base-pairings between C266-A268 and U307-G309 in the P7 of the Tetrahymena ribozyme is nonessential for the in vitro self-splicing reaction

P7 is highly conserved in Group I self-splicing intron ribozymes. This regi on is known to coordinate metal ions and bind a cofactor guanosine required for the self-splicing, To further investigate the fundamental role of the corresponding region in the Tetrahymena ribozyme, we attempted to identify minimal requirements for the base-paired region excluding the guanosine bin ding site. We discovered that a variety of sequences are eligible and its d erivatives possessing extra nucleotide(s) can still conduct the first step of splicing, indicating that no particular base-pairing is essential in thi s region for conducting the reaction in vitro. The results provide two hypo theses for the fundamental role of this region: (i) if the region contains element(s) that are strictly required in the catalysis, they are not necess arily tightly fixed in the ribozyme and (ii) if not, its fundamental role m ay simply be to coordinate neighboring regions that are directly involved i n the catalysis. (C) 2001 Academic Press.