Two group I introns with a C.G basepair at the 5' splice-site instead of the very highly conserved U.G basepair: is selection post-translational?

AUTOR(ES)

Hur, M

RESUMO

In virtually all of the 200 group I introns sequenced thus far, the specificity of 5' splice-site cleavage is determined by a basepair between a uracil base at the end of the 5' exon and a guanine in an intron guide sequence which pairs with the nucleotides flanking the splice-site. It has been reported that two introns in the cytochrome oxidase subunit I gene of Aspergillus nidulans and Podospora anserina are exceptions to this rule and have a C.G basepair in this position. We have confirmed the initial reports and shown for one of them that RNA editing does not convert the C to a U. Both introns autocatalytically cleave the 5' splice-site. Mutation of the C to U in one intron reduces the requirement for Mg2+ and leads to an increase in the rate of cleavage. As the C base encodes a highly conserved amino acid, we propose that it is selected post-translationally at the level of protein function, despite its inferior splicing activity.

Documentos Relacionados

• The conserved U.G pair in the 5' splice site duplex of a group I intron is required in the first but not the second step of self-splicing.
• Initial recognition of U12-dependent introns requires both U11/5′ splice-site and U12/branchpoint interactions
• RNA structure, not sequence, determines the 5' splice-site specificity of a group I intron.
• Suppression of mammalian 5' splice-site defects by U1 small nuclear RNAs from a distance.
• Accurate 5' splice-site selection in mouse kappa immunoglobulin light chain premessenger RNAs is not cell-type-specific.