PARENT SESSION
1:30 PM to 3:30 PM
Tuesday, April 23, 2002
Poster Session 24 Signal Transduction
Room: Nevada Exhibition Center

(P29-287) CHARACTERIZATION OF A NOVEL RADIATION RESPONSIVE PROTEIN KINASE .

Kodym, Reinhard^*,1, Thomas, Mayerhofer¹, Elfriede, Hoerth¹, ¹ Department for Radiobiology, Vienna, Austria

ABSTRACT-
We have previously reported the detection of a novel protein kinase activity, which is downregulated within minutes after exposure of HL-60 cells to ionizing radiation. The kinase activity, which we named pK90, was detected at a relative molecular mass of 90 kDa using an in gel renaturation assay. We found that a drop in the activity can be found within 5 minutes after irradiation with doses as low as 2 Gy. PK90 is a nuclear serine/threonine kinase which is able to phosphorylate numerous substrates. Blocking experiments of alkaline phosphatase catalyzed dephosphorylation of pk90 with antibodies directed against phospho-threonine and phospho-tyrosine indicated that a phosphorylation of both amino acids is required for full kinase activity. Using a calibrated gel filtration chromatography column the native molecular mass of pK90 was determined to be about 400 kDa, indicating the presence of pK90 in a multi protein complex in the cell. During attempts to purify pK90 activity to homogeneity we found that a non-protein cofactor is required for kinase activity. This cofactor was discovered to be DNA. Purification and peptide mapping of pK90 is currently performed. We conclude that because of its properties pK90 might be an important kinase involved in signaling of radiation induced DNA damage.

KEYWORDS: protein kinase, DNA