A single point mutation in the yeast TRP4 gene affects efficiency of mRNA 3 ' end processing and alters selection of the poly(A) site

The yeast TRP4 mRNA 3' end formation element is a bidirectional element whi ch functions in both orien tations in an artificial in vivo test system. In this study the role of 3' end formation was analysed in the context of the entire TRP4 gene. The 3' untranslated region (3'UTR) of TRP4 was altered a nd changes were analysed for their influence on TRP4 gene expression. The 3 'UTR in reverse orientation was fully functional and did not affect TRP4 ge ne expression. Exchanging the TRP4 3'UTR by the bidirectional ARO4 or the u nidirectional GCN4 3' end formation element allowed efficient gene expressi on. Deletion of the entire TRP4 3'UTR resulted in 70% reduction of TRP4 mRN A and 50% reduced specific Trp4 enzyme activity in comparison to wild-type. A single point mutation within the TRP4 3'UTR caused the same effect on ge ne expression. This point mutation did not only affect the efficiency of 3' end formation, but also produced new poly(A) sites which were situated ups tream of the wild-type poly(A) sites. Therefore this sequence motif in the TRP4 3'UTR acts simultaneously as both an efficiency and positioning elemen t.