Plays as essential role in regulating terminal differentiation. First accumulates at 8 hours of development and is maintained in both prespore and prestalk cells until culmination when it is found only is stalk cells. During the mound stage, equally abundant in all cells, whereas during the finger/migrating slug stage, expression is somewhat higher in the anterior prestalk region. During culmination predominantly seen in the descending stalk tube. Null cells are arrested at the tight mound stage but accumulate the bright yellow pigment characteristic of mature sori. Although these mutant strains do not form fruiting bodies, many of the cells encapsulate within the mounds. Sporulation occurs about 6 hours earlier, accompanied by precocious expression of a prespore gene, spiA. However, the spores are defective and lose viability over a period of several hours. Unencapsulated cells also die unless they are dissociated from the mounds and shaken in suspension.