In vitro polyadenylation is stimulated by the presence of an upstream intron.
The majority of vertebrate pre-mRNAs are both spliced and polyadenylated. To investigate the mechanism whereby processing factors recognize last exons containing both splicing and polyadenylation consensus elements, chimeric precursor RNAs containing a single intron and a poly(A) site were constructed and assayed for in vitro splicing and polyadenylation. Chimeric RNAs underwent splicing and polyadenylation. Both reactions occurred in a single RNA. The presence of an intron enhanced the rate of polyadenylation at a downstream poly(A) site. The extent of stimulation varied from two- to fivefold, depending on the magnesium concentration. Maximal stimulation of polyadenylation by an upstream intron required a 3' splice site but not a 5' splice site, suggesting that the structure of the terminal exon was more important than the presence of a complete upstream intron. We suggest that splicing and polyadenylation factors interact to recognize terminal, poly(A) site-containing exons. Such interaction may explain why all known intron-containing eukaryotic pre-mRNAs generate their 3' ends by polyadenylation.
Marrs McClean Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030.
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D001483:Base Sequence; D002467:Cell Nucleus / Q000378:metabolism; D002474:Cell-Free System; D005091:Exons / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D007438:Introns / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D011061:Poly A / Q000096:biosynthesis*; D012313:RNA / Q000235:genetics; D012322:RNA Precursors / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional / Q000235:genetics*; D012326:RNA Splicing / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis*; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics
D012322:RNA Precursors; D012333:RNA, Messenger; C039919:RNA, recombinant; D011061:Poly A; D012313:RNA