The biosynthesis and function of eukaryotic mRNAs requires
a series of events including nuclear polyadenylation, transport
to the cytoplasm, translation, and ultimately mRNA degradation.
To identify the interrelationships between these events,
we examined the synthesis and fate of mRNAs in several
strains defective in mRNA export. Strains carrying lesions
in RAT7, GLE1, MEX67, and RAT8,
produce nascent transcripts carrying poly(A) tails roughly
30 residues longer than the nascent poly(A) tails observed
in wild type. In the rat7-1, rat8-2,
and mex67-5 strains, the hyperadenylated transcripts
undergo a novel form of deadenylation to chase into a population
with normal poly(A) tail lengths, which cofractionate with
polysomes, undergo nonsense-mediated decay, and are degraded
by the normal cytoplasmic decay machinery. This suggests
a relationship between the mechanism of processing to a
normal poly(A) tail length and the ability of these transcripts
to proceed in their metabolism. These observations provide
further support for the view that mRNA 3′-end formation
and mRNA export are mechanistically coupled events.