A Protein Kinase Isolated from Porcine Brain Microvessels is Similar to a Class of Heat‐Shock Proteins

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Abstract
To further characterize a protein kinase present in porcine brain microvessels, a cDNA library using porcine microvessel poly(A) RNA was screened with polyclonal antibodies raised against the native protein kinase. Since no full‐length cDNA clone could be obtained, the missing sequence information was completed using two subsequent polymerase chain reactions. The amplified transcripts were cloned and the sequence determined. Additionally, a genomic DNA library from porcine kidney was screened to substantiate the results obtained from the polymerase chain reaction. Earlier hints of a relation to a subclass of the family of heat‐shock proteins (HSPs) based upon a close sequence similarity at its amino‐terminus could be confirmed by comparison of the full‐length cDNA sequences. Common protein kinase consensus sequences, a targeting sequence for proteins of the endoplasmic reticulum at the carboxy‐terminus as well as a hydrophobic leader sequence in the amino‐terminal region of the protein could also be identified. Furthermore, a set of membrane‐associated substrate proteins of this enzyme could be detected in brain capillaries. The results indicate that at least some members of the HSP 90 subfamily undergo autophosphorylation and show protein kinase activity by phosphorylating substrate proteins in vitro.