Improperly processed mRNAs are degraded in the nucleus by which complex?

The exosome complex plays a critical role in the degradation of improperly processed mRNAs in the nucleus. This multi-protein complex has a primary function in the recognition and degradation of RNA molecules that are faulty or defective, ensuring that only properly processed and functional mRNAs are available for translation. The exosome recognizes and binds to these aberrant RNA transcripts, often those that have not been capped correctly, spliced, or polyadenylated, and proceeds to degrade them through exonuclease activity.

In contrast, the ribosome is involved in translating mRNA into proteins, the proteasome is responsible for degrading proteins rather than RNA, and the spliceosome primarily functions in the maturation of pre-mRNA through the removal of introns. Thus, they do not engage in the degradation of improperly processed mRNAs. This specificity of the exosome for RNA surveillance highlights its importance in maintaining RNA quality control within the cell.