CLONING AND SEQUENCING OF THE CDNA-ENCODING THE AVIAN KIDNEY CAMP-DEPENDENT PROTEIN-KINASE INHIBITOR PROTEIN

The endogenous inhibitor of cAMP-dependent protein kinase (PKA) is dow n-regulated in the kidneys from vitamin-D-replete chicks as compared t o vitamin-D-deficient chicks. Screening of a vitamin-D-deficient chick kidney library resulted in the isolation of a 450-bp cDNA clone encod ing the 76-amino acid (aa) protein kinase inhibitor (PKI). The deduced aa sequence of avian PKI shares 80 and 41% identity with the mammalia n PKI alpha and PKI beta 1 isoforms, respectively. The chick and mamma lian PKI contain conserved N-terminal sequences, including the pseudo- substrate site ((18)GRRNA(22)), which are required for potent inhibiti on of the catalytic subunit of PKA. Chick kidney PKI contains ten uniq ue aa in the C-terminal portion of the protein that are not shared wit h the mammalian PKI alpha or beta isoforms.