PROTEIN SPLICING OF THE YEAST TFP1 INTERVENING PROTEIN-SEQUENCE - A MODEL FOR SELF-EXCISION

Protein splicing is the protein analogue of RNA splicing in which the central portion (spacer) of a protein precursor is excised and the ami no- and carboxy-terminal portions of the precursor reconnected. The ye ast Tfp1 protein undergoes a rapid protein splicing reaction to yield a spliced 69 kDa polypeptide and an excised 50 kDa spacer protein. We have demonstrated that the 69 kDa species arises by reformation of a b ona fide peptide bond. Deletion analyses indicate that only sequences in the central spacer protein of the Tfp1 precursor are critical for t he protein splicing reaction. A fusion protein in which only the Tfp1 spacer domain was inserted into an unrelated protein also underwent ef ficient splicing, demonstrating that all of the information required f or protein splicing resides within the spacer domain. Alteration of Tf p1p splice junction residues blocked or kinetically impaired protein s plicing. A protein splicing model is presented in which asparagine rea rrangement initiates the self-excision of the spacer protein from the Tfp1 precursor. The Tfp1 spacer protein belongs to a new class of inte rvening sequences that are excised at the protein rather than the RNA level.