Effects on mRNA splicing of mutations in the 3' region of the Saccharomyces cerevisiae actin intron.

Point mutations, deletions, and a sequence context change were introduced at positions 3' to the internal conserved TACTAAC sequence of the Saccharomyces cerevisiae actin intron. In vivo analysis of yeast mRNA splicing suggests that, in contrast to the importance of the polypyrimidine tract in metazoan introns, specific sequences in this region are not required for efficient excision of a yeast intron. However, a double point mutation near the 3' junction (GG/AC) does severely inhibit splicing. Although this mutagenesis of the 3' junction, as well as deletion of most nucleotides between the TACTAAC and the 3' junction, caused only a slight accumulation of primary transcript, the observed accumulation of lariat intermediate by these mutants demonstrates the significance of this region for a step(s) in the splicing process after lariat formation.