Which proteins must be lost from immature mRNA for successful export?

For successful export of immature mRNA from the nucleus to the cytoplasm, proteins involved in RNA splicing must be removed. During the maturation process of mRNA, introns are spliced out, and the resulting exons are joined together. The proteins that facilitate this splicing, such as the spliceosomal components, are essential during the processing of pre-mRNA but must be released after splicing is complete to allow the mature mRNA to be properly recognized and exported by the nuclear pore complex.

In contrast, other proteins have different roles in the life cycle of mRNA. Poly-A binding proteins play a crucial role in the stability and translation of mature mRNA by binding to the poly-A tail. RNA polymerase is the enzyme that synthesizes RNA from the DNA template during transcription and is not involved in the removal process for export. Translation factors, on the other hand, are associated with the ribosomes and facilitate the translation of mRNA into protein once it is in the cytoplasm. Thus, the key proteins that must be lost for the mRNA to successfully exit the nucleus are those associated with the splicing processes.