Tight binding of the 5′ exon to domain I of a group II self-splicing intron requires completion of the intron active site

Maria Costa (1) , François Michel

1 I2BC - Institut de Biologie Intégrative de la Cellule

Group II self-splicing requires the 5' exon to form base pairs with two stretches of intronic sequence (EBS1 and EBS2) which also bind the DNA target during retrotransposition of the intron. We have used dimethyl sulfate modification of bases to obtain footprints of the 5' exon on intron Pl.LSU/2 from the mitochondrion of the alga Pylaiella littoralis, as well as on truncated intron derivatives. Aside from the EBS sites, which are part of the same subdomain (ID) of ribozyme secondary structure, three distant adenines become either less or more sensitive to modification in the presence of the exon. Unexpectedly, one of these adenines in subdomain IC1 is footprinted only in the presence of the distal helix of domain V, which is involved in catalysis. While the loss of that footprint is accompanied by a 100-fold decrease in the affinity for the exon, both protection from modification and efficient binding can be restored by a separate domain V transcript, whose binding results in its own, concise footprint on domains I and III. Possible biological implications of the need for the group II active site to be complete in order to observe high affinity binding of the 5' exon to domain I are discussed.

Mots clés: 5' exon footprints; group II intron; intron-exon interactions; methylation probing; ribozyme; group II intron intron-exon interactions methylation probing ribozyme 5' exon footprints

Domaines: Sciences du Vivant [q-bio]

Maria Costa, François Michel. Tight binding of the 5′ exon to domain I of a group II self-splicing intron requires completion of the intron active site. EMBO Journal, 1999, 18, pp.1025 - 1037. ⟨10.1093/emboj/18.4.1025⟩. ⟨hal-03914605⟩