Mutation of the AAUAAA polyadenylation signal depresses in vitro splicing of proximal but not distal introns.

To investigate the relationship between splicing and polyadenylation during the production of vertebrate mRNAs, we examined the effect of mutation of a poly(A) site on splicing of upstream introns. Mutation of the AAUAAA polyadenylation consensus sequence inhibited in vitro splicing of an upstream intron. The magnitude of the depression depended on the magnesium concentration. Dependence of splicing on polyadenylation signals suggests the existence of interaction between polyadenylation and splicing factors. In multi-intron precursor RNAs containing duplicated splice sites, mutation of the poly(A) site inhibited removal of the last intron, but not the removal of introns farther upstream. Inhibition of removal of only the last intron suggests segmental recognition of multi-exon precursor RNAs and is consistent with previous suggestions that signals at both ends of an exon are required for effective splicing of an upstream intron.