Protein splicing is an intramolecular reaction of a particular protein in which an internal protein segment (called an intein) is removed from a precursor protein with a ligation of C-terminal and N-terminal external proteins (called exteins) on both sides. The splicing junction of the precursor protein is mainly a cysteine or a serine, which are amino acids containing a nucleophilic side chain. The protein splicing reactions which are known now do not require exogenous cofactors or energy sources such as adenosine triphosphate (ATP) or guanosine triphosphate (GTP). Normally, splicing is associated only with pre-mRNA splicing.
Types of inteins
The type of the splicing proteins is categorized into four classes: maxi-intein, mini-intein, trans-splicing intein, and alanine intein. Maxi-inteins are N- and C-terminal splicing domains containing an endonuclease domain. The mini-inteins are typical N- and C-terminal splicing domains; however, the endonuclease domain is not present. In trans-splicing inteins, the intein is split into two (or perhaps more) domains, which are then divided into N-termini and C-termini. Alanine inteins have the splicing junction of an alanine instead of a cysteine or a serine, in both of which the protein splicing occurs.
Protein splicing was unanticipated and discovered by two groups (Anraku  and Stevens ) in 1990. They both discovered a Saccharomyces cerevisiae VMA1 in a precursor of a vacuolar H+-ATPase enzyme. The amino acid sequence of the N- and C-termini corresponded to 70% DNA sequence of that of a vacuolar H+-ATPase from other organisms, while the amino acid sequence of the central position corresponded to 30% of the total DNA sequence of the yeast HO nuclease.
- Hirata R, Ohsumk Y, Nakano A, Kawasaki H, Suzuki K, Anraku Y (April 1990). "Molecular structure of a gene, VMA1, encoding the catalytic subunit of H(+)-translocating adenosine triphosphatase from vacuolar membranes of Saccharomyces cerevisiae". J. Biol. Chem. 265 (12): 6726–33. PMID 2139027.
- Kane PM, Yamashiro CT, Wolczyk DF, Neff N, Goebl M, Stevens TH (November 1990). "Protein splicing converts the yeast TFP1 gene product to the 69-kD subunit of the vacuolar H(+)-adenosine triphosphatase". Science. 250 (4981): 651–7. doi:10.1126/science.2146742. PMID 2146742.