Characterization of PKIγ, a Novel Isoform of the Protein Kinase Inhibitor of cAMP-dependent Protein Kinase

摘要: Attempts to understand the physiological roles of protein kinase inhibitor (PKI) proteins have been hampered by a lack knowledge concerning molecular heterogeneity PKI family. The PKIgamma cDNA sequence determined here predicted an open reading frame 75 amino acids, showing 35% identity PKIalpha and 30% PKIbeta1. Residues important for high affinity PKIbeta1 as well nuclear export catalytic (C) subunit cAMP-dependent were found be conserved in PKIgamma. Northern blot analysis showed that 1.3-kilobase message is widely expressed, with highest levels heart, skeletal muscle, testis. RNase protection revealed most tissues examined expressed at equal or higher than other known isoforms several mouse-derived cell lines, predominant message. Partial purification activities from mouse heart DEAE ion exchange chromatography resolved two major inhibitory peaks, isoform-specific polyclonal antibodies raised against recombinant identified these A comparison potencies Escherichia coli was potent competitive Calpha phosphotransferase activity vitro (Ki = 0.44 nM) but 6-fold less 0.073 nM). Like PKIalpha, capable blocking accumulation Flag-tagged C transiently transfected mammalian cells. Finally, murine gene overlap adenosine deaminase on chromosome 2. These results demonstrate novel, functional isoform accounts previously observed discrepancy between mRNA tissues.