Entry into the stationary phase requires the yeast BCY1 gene, which en
codes the regulatory subunit of the cAMP-dependent protein kinase (cAP
K). New bcy1 mutants, constructed by in vitro mutagenesis of the 3'-re
gion encoding the cAMP-binding domains, were classified as early or la
te-acting mutants based on viability studies. The late-acting bcy1 mut
ants accumulated fewer stationary phase-specific Bcy1p isoforms and ha
d decreased cAPK activity. This late-acting class is novel and dies af
ter 7 days in culture, later than two previously reported stationary p
hase mutants, ubi4 and ard1.