Splice Donor and Acceptor Sites

Splice donor and acceptor sites are specific nucleotide sequences that define the boundaries between exons and introns during RNA splicing. Donor sites, located at the 5′ end of an intron (exon-intron boundary), are typically characterized by the dinucleotide GT. Acceptor sites, located at the 3′ end of an intron (intron-exon boundary), are typically characterized by the dinucleotide AG. These sequences are crucial for the proper excision of introns and ligation of exons during mRNA processing. 

Elaboration:

• Donor Site (5′ Splice Site): This site marks the beginning of an intron and the end of the preceding exon. The most common donor site sequence is GT (GU in pre-mRNA). 
• Acceptor Site (3′ Splice Site): This site marks the end of an intron and the beginning of the following exon. The most common acceptor site sequence is AG. 
• Splicing Process: During RNA splicing, the spliceosome (a complex of proteins and RNA) recognizes these splice sites. It cleaves the pre-mRNA at the donor site, forms a lariat structure with the intron, and then cleaves at the acceptor site, releasing the intron and joining the exons together. 
• Importance of Splice Sites: Mutations or alterations at these sites can disrupt normal splicing, leading to the inclusion of intronic sequences in the mature mRNA or the skipping of exons, which can result in non-functional proteins.