MAMMALIAN CAMP-DEPENDENT PROTEIN-KINASE FUNCTIONALLY REPLACES ITS HOMOLOG IN YEAST

The cDNA encoding the catalytic subunit (C-alpha) from mouse cAMP-dependent protein kinase (PK) was expressed in Saccharomyces cerevisiae. By a plasmid swap procedure, we demonstrated that the mammalian C-alpha subunit can functionally replace its yeast homolog to maintain the viability of a yeast strain containing genetic disruptions of the three TPK genes encoding the yeast C subunits. C-alpha subunit produced in yeast was purified and its biochemical properties were determined. The protein isolated from yeast appears to be myristylated, as has been found for C subunits from higher eukaryotic cells. This system would be useful for studying the biochemistry of the mammalian enzyme in vitro and its biological role in a model in vivo system. These studies demonstrate that the PK substrate(s) required for viability are recognized by the mammalian enzyme. In general terms, these results demonstrate that heterologous proteins with only 50% sequence conservation with their yeast counterparts can be functional in yeast. This is an important result because it validates the use of yeast to identify the biological role of newly cloned genes from heterologous systems, a key tenet of the Human Genome Initiative.