Pre-mRNA splicing imprints mRNA in the nucleus with a novel RNA-binding protein that persists in the cytoplasm

We describe a novel RNA binding protein, Y14, a predominantly nuclear nucle ocytoplasmic shuttling protein. Interestingly, Y14 associates preferentiall y with mRNAs produced by splicing but not with pre-mRNAs, introns, or mRNAs produced from intronless cDNAs. Y14 associates with both nuclear mRNAs and newly exported cytoplasmic mRNAs. Splicing of a single intron is sufficien t for Y14 association. Y14-containing nuclear complexes are different from general hnRNP complexes. They contain hnRNP proteins and several unique pro teins including the mRNA export factor TAP. Thus, Y14 defines novel interme diates in the pathway of gene expression, postsplicing nuclear preexport mR NPs, and newly exported cytoplasmic mRNPs, whose composition is established by splicing. These findings suggest that pre-mRNA splicing imprints mRNA w ith a unique set of proteins that persists in the cytoplasm and thereby com municates the history of the transcript.