The Y14 protein communicates to the cytoplasm the position of exon-exon junctions

We recently described an RNA-binding protein, Y14, that binds preferentiall y to spliced mRNAs and persists in the cytoplasm, Y14 is part of a multi-pr otein complex that also contains the mRNA export factor TAP. This suggests that splicing imprints the mRNA with a unique set of proteins that communic ate the history of the transcript to the cytoplasm, Here, using microinject ion of pre-mRNAs into Xenopus oocyte nuclei followed by immunoprecipitation of RNase-fragmented mRNAs from the cytoplasm, we show that Y14 is stably b ound to sequences immediately upstream of exon-exon junctions. This feature appears to be unique to Y14, Using monoclonal antibodies that we produced against Aly/REF, another component recently reported to be an mRNA export f actor, we show that Aly/REF is associated with spliced mRNAs in the nucleus but is not detectable on mRNAs in the cytoplasm, Thus, we propose that the splicing-dependent binding of Y14 provides a position-specific molecular m emory that communicates to the cytoplasm the location of exon and intron bo undaries. This novel mechanism may play an important role in post-splicing events.