What type of sequences are primarily removed during RNA splicing?

During RNA splicing, it is the introns that are primarily removed. Introns are non-coding sequences found within a gene that do not contribute to the final protein product. They are interspersed among exons, which are the coding sequences that will be translated into protein.

The reason introns are removed is to create a mature mRNA molecule that contains only the exons, which are essential for the synthesis of functional proteins. Human genes often contain multiple introns, and the precise removal of these sequences is critical for the correct expression of genes. The splicing process ensures that the exons are joined together in the appropriate order, allowing for the correct coding sequence for the protein.

On the other hand, exons, which are the coding regions, are retained and become part of the final mRNA. Promoters are regulatory sequences that initiate transcription but are not involved in RNA splicing. Terminator sequences signal the end of transcription and similarly are not spliced out of the RNA transcript. Therefore, the focus of splicing is specifically on the removal of introns to generate a functional mRNA ready for translation.