Inhibitor that slows proliferation of secreting cells (also known as chalone). Requires aprA for activity. Interacts with aprA. Concentrated in subcellular structures, possibly vesicles. Expressed at highest levels in vegetatively growing cells and declines during development (at protein level). Cells proliferate more rapidly than wild type cells and exhibit supernumerary centrosomes and a cytokinesis defect. They also produce fewer spores at culmination. Form large fruiting bodies with large spore heads. Belongs to the peptidase C1 family. Lacks catalytic activity, even though the active site residues are conserved.