Final answer:
RNA editing can create different protein forms and introduce new spliceosome recognition sites by altering nucleotides within mRNA, possibly as an ancient mechanism of gene regulation.
Step-by-step explanation:
RNA editing can result in different proteins as well as new spliceosome recognition sites. This editing process can change some of the nucleotides in mRNA, altering the protein that is produced. For example, the human protein known as APOB has two forms because RNA editing creates a premature stop signal in some mRNAs, leading to a smaller protein. Additionally, RNA editing may introduce changes in the spliceosome recognition sequence, potentially adding new sites for the spliceosome to act. This could be an evolutionary remnant of ancient RNA-based gene regulation systems, particularly within mitochondria that are thought to have descended from prokaryotes. Mutations in spliceosome components can also lead to changes in splicing patterns, potentially creating diverse protein outcomes from a single gene.