Abstract: Entry into the stationary phase requires the yeast BCY1 gene, which encodes the regulatorysubunit of the cAMP-dependent protein kinase (cAPK). New bcy1 mutants, constructed by in vitro mutagenesis of the 3'-region encoding the cAMP-binding domains, were classified as early or late-acting mutants based on viability studies. The late-acting bcy1 mutants accumulated fewer stationary phase-specific Bcy1p isoforms and had decreased cAPK activity. This late-acting class is novel and dies after 7 days in culture, later than two previously reported stationary phase mutants, ubi4 and ard1.