Revertants of a trans-dominant S49 mouse lymphoma mutant that affects expression of cAMP-dependent protein kinase

Phenotypic revertants were isolated from an S49 mouse lymphoma tissue culture cell mutant that lacks cAMP-dependent protein kinase (cA-PK) activity (kin^-). The mutant phenotype is trans-dominant and results from a lesion that probably lies outside the cA-PK subunit structural genes. The nature of the event that produces the kin^- phenotype is unknown. However, the mechanism that is responsible for its behavior is genetically encoded because: spontaneous revertants arise at low frequency; reversion frequency is increased by mutagen treatment; mutagen-specific classes of revertant phenotypes are induced; and some revertants are temperature-sensitive for expression of cA-PK subunit polypeptides. Additional evidence is provided that argues against structural lesions in cA-PK catalytic (C) subunits as explanatory of the kin^- phenotype. Kin^- cells do not express an immunologically detectable C polypeptide, whereas C expression is restored in revertant cells. Revertants in which phenotype and cA-PK activity levels are only partially restored to that of wild-type cells contain a commensurately reduced amount of C polypeptide. Finally, the structure of C polypeptide in partial revertants is unaltered from that of wild-type C. The evidence supports the hypothesis that the kin^- lesion defines a regulatory gene responsible for setting intracellular levels of cA-PK C subunit expression.