Self-catalyzed cleavage of the yeast nucleoporin Nup145p precursor

Nup145p is a component of the nuclear pore complex of Saccharomyces cerevis iae and is essential for mRNA export. Nup145p and its apparent vertebrate h omologue are the only known nucleoporins to be composed of two functionally independent peptide moieties resulting from the post-translational cleavag e of a large precursor molecule. In this study, the proteolytic cleavage si te of Nup145p has been mapped upstream of an evolutionary conserved serine residue. Cleavage occurs at the same site when a precursor is artificially expressed in Escherichia coil. A hydroxyl-containing residue is critical fo r the reaction, although a thiol-containing residue offers an acceptable re placement. In vitro kinetics experiments using a purified precursor molecul e demonstrate that the cleavage is self-catalyzed and that the catalytic do main lies within the N-terminal moiety. Taken altogether, our data are cons istent with a proteolytic mechanism involving an N > 0 acyl rearrangement a nd a subsequent ester intermediate uncovered in other self-processing prote ins.