and archaea) and in viruses.

Protein splicing was unanticipated and its mechanisms were 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