Which complex is essential for marking properly spliced RNA?

The exon junction complex (EJC) plays a critical role in the maturation of RNA after splicing. This multi-protein complex is deposited onto mRNA transcripts at the junction of exons, specifically marking the areas where introns have been removed. The presence of the EJC is essential for several downstream processes, including the export of mRNA from the nucleus to the cytoplasm, the regulation of mRNA translation, and the surveillance mechanisms that oversee mRNA quality control.

By marking properly spliced RNA, the EJC assists in distinguishing mature mRNA from improperly processed transcripts, which might still contain intronic sequences. This is vital for ensuring that only correctly spliced and viable mRNA is translated into proteins, thus maintaining cellular function and preventing errors that could arise from faulty mRNA.

While the other choices relate to RNA and its processing or transport within the cell, they do not serve the specific purpose of marking spliced RNA. RNA polymerase is involved in transcription, RNA binding proteins often have roles in the stabilization or transport of RNA, and nuclear pore complexes facilitate the transport of RNA out of the nucleus, but they do not directly mark spliced RNA. The unique function of the EJC makes it integral to the recognition and use of properly