Abstract
Nucleophosmin (NPM), an abundant, predominantly nucleolar protein that influences numerous cellular processes, was shown to specifically associate with the bodies of messenger RNAs as a result of the process of 3'-end formation. NPM deposition requires polyadenylation but not the 3' cleavage event to occur on the transcript. Furthermore, the protein does not associate with RNAs bearing a preformed poly(A) tail or with mRNAs that have undergone cleavage but not polyadenylation. A region within 10 bases upstream of the AAUAAA element is required for NPM association, but deposition of the protein seems to be sequence independent. NPM association with poly(A)(+) mRNAs was also demonstrated in vivo. NPM, therefore, represents a mark left on transcripts as a result of 3'-end processing and may have a role in one or more of a variety of post-transcriptional processes influenced by the polyadenylation event.