Multiple Ca2+/calmodulin‐dependent protein kinase genes in a unicellular eukaryote

We purified a Ca2+/calmodulin (CaM)‐dependent protein kinase (CaM kinase) from the yeast Saccharomyces cerevisiae with properties similar to mammalian type II CaM kinases. Degenerate oligonucleotides designed on the basis of the amino acid sequence of tryptic peptides from the 55 kd subunit of the yeast CaM kinase were used to isolate its gene from a set of lambda gt11‐yeast genomic DNA phage clones initially selected by the ability to bind 125I‐labelled yeast CaM. The cloned gene (CMK1) encodes an open reading frame that is homologous to the sequences of vertebrate type II CaM kinases. Several criteria demonstrated that the CMK1 gene product is the 55 kd polypeptide. Neither over‐production (11‐fold) nor complete elimination of the CMK1 gene product had any detectably deleterious effect on yeast cell growth. Extracts from cmk1 delta cells, which lacked detectable p55 using an antiserum raised against a Staphylococcus aureus protein A‐CMK1 fusion protein, possessed significant residual Ca2+/CAM‐dependent protein kinase activity. Using the CMK1 gene as a probe at low stringency, a second gene (CMK2) encoding another CaM‐dependent protein kinase with striking sequence similarity to CMK1 was cloned. Deletion of CMK2, or both CMK1 and CMK2, was not lethal, although loss of CMK2 caused a slow rate of spore germination.