Abstract
We have characterized transcripts synthesized in vivo by
bacteriophage T7 RNA polymerase to investigate yeast mRNA
processing. T7 transcripts are not capped, consistent with capping
being tightly coupled to RNA polymerase II (pol II) transcription.
In contrast to higher eukaryotic non-pol II transcripts, yeast
T7 transcripts are spliced as well as cleaved and polyadenylated.
However, T7 and pol II transcripts are affected differently
in cleavage and polyadenylation mutant strains, indicating that
pol II may have a role in yeast 3′ end formation. T7
transcripts with 3′ ends directed by a polyadenylation
signal are exported from the nucleus, and this export is dependent
on the canonical cleavage and polyadenylation machinery.
Importantly, transcripts with T7 terminator-directed 3′
ends are unadenylated and predominantly nuclear in wild-type
cells. Our results suggest that transcription by pol II is required
for neither the nuclear export of an in vivo-transcribed mRNA
nor for the retention of transcripts with aberrant 3′
ends. Moreover, proper 3′ end formation may be necessary
and sufficient to promote mRNA export in yeast.