A 26-nt sequence from the 3' UTR of the yeast GAL7 mRNA directs accura
te and efficient cleavage and polyadenylation to form the 3' end of th
e GAL7 mRNA in vivo and in vitro. Here we asked whether this polyadeny
lation signal can function within the context of a tRNA. Insertion of
the GAL7 signal into the intron of the dominant SUP4 nonsense suppress
or allowed us to judge the effect of the insert on SUP4 function by ob
servation of nonsense suppression efficiency in vivo. The GAL7 signal
impairs the function of SUP4 in an orientation-dependent manner in viv
o, consistent with its ability to specify cleavage and polyadenylation
in this context in vitro. Mutation of a UA repeat within the GAL7 sig
nal restores SUP4 function partially, consistent with the role of this
repeat as an efficiency element in polyadenylation. Mutations that im
pair the mRNA 3' end-processing factors Rna14p and Rna15p restore supp
ressor function partially. Northern blot analysis, PCR amplification,
and DNA sequence analysis show that the GAL7 signal directs polyadenyl
ation within the body of pre-SUP4 and within the terminator, suggestin
g that polyadenylation inhibits 5' and 3' end processing, as well as r
emoval of the pre-tRNA intron. These findings indicate that the GAL7 p
olyadenylation signal is capable of targeting a pre-tRNA to the mRNA p
rocessing pathway.