Characterization of the polyadenylation signal from the T-DNA-encoded octopine synthase gene.

We have characterized the polyadenylation signal from the octopine synthase (ocs) gene. This signal directs mRNA 3' end formation at a number of distinct sites. A combination of deletion and linker-substitution analyses revealed that each of these sites is controlled by multiple upstream sequence elements. Upstream sequences relatively far (greater than 80 nt) from the ocs poly[A] sites were found to be needed for functioning of these sites. Upstream sequences nearer to poly [A] sites were also found to be involved in mRNA 3' end formation in the ocs gene. In addition, a set of novel elements that mediates 3' end choice was uncovered by deletion analysis of sequences downstream from the ocs polyadenylation sites. Our experiments indicate mRNA 3' end formation in the ocs is controlled by a complex series of cis-acting signals, and suggest that the process of mRNA 3' end formation might be linked to transcription termination.