Upstream sequences other than AAUAAA are required for efficient messenger RNA 3′-end formation in plants

Abstract

We have characterized the upstream nucleotide sequences involved in mRNA 3′-end formation in the 3′ regions of the cauliflower mosaic virus (CaMV) 19S/35S transcription unit and a pea gene encoding ribulose-1,5-bisphosphate carboxylase small subunit (rbcS). Sequences between 57 bases and 181 bases upstream from the CaMV polyadenylation site were required for efficient polyadenylation at this site. In addition, an AAUAAA sequence located 13 bases to 18 bases upstream from this site was also important for efficient mRNA 3′-end formation. An element located between 60 bases and 137 bases upstream from the poly(A) addition sites in a pea rbcS gene was needed for functioning of these sites. The CaMV - 181/-57 and rbcS -137/-60 elements were different in location and sequence composition from upstream sequences needed for polyadenylation in mammalian genes, but resembled the signals that direct mRNA 3′-end formation in yeast However, the role of the AAUAAA motif in 3′-end formation in the CaMV 3′ region was reminiscent of mRNA polyadenylation in animals. We suggest that multiple elements are involved in mRNA 3′-end formation in plants, and that interactions of different components of the plant polyadenylation apparatus with their respective sequence elements and with each other are needed for efficient mRNA 3′-end formation.