Identification of the catalytic subunit of cAMP-dependent protein kinase from the photosynthetic flagellate, Euglena gracilis Z

A gene named epk2 that encodes the amino acid sequence of a protein kinase was identified from the photosynthetic flagellate, Euglena gracilis Z, Homo logy search and phylogenetic analysis revealed that the deduced amino acid sequence of epk2 is most similar to that of the catalytic subunit of cAMP-d ependent protein kinase (PKA), Northern blot analysis showed that Euglena c ells express a 1,4-kb transcript of this gene. When the EPK2 protein was co expressed with the rat regulatory subunit of PKA in cultured mammalian cell s, these two proteins were coimmunoprecipitated. The association of EPK2 an d the rat regulatory subunit of PKA was not detected in the cell lysate inc ubated with cAMP, EPK2 immunoprecipitated from the transfected cells phosph orylated Kemptide, a synthetic peptide substrate for PKA, and the phosphory lation was inhibited by PKI, a PEA-selective protein kinase inhibitor. Thes e results indicate that EPK2 is a PKA homologue in the photosynthetic flage llate, and this is the first evidence for the occurrence of the PKA catalyt ic subunit in photosynthetic organisms. (C) 1999 Federation of European Bio chemical Societies.