Ku protein in human T and B lymphocytes: full length functional form and signs of degradation

DNA-dependent protein kinase (DNA-PK) has been shown to take part in cell c ycle regulatory signal transduction and in the repair of X-ray-induced DNA double-strand breaks. Functional DNA-PK is furthermore needed for the gener ation of antigen specificity during lymphocyte maturation. The Ku86 subunit of DNA-PK has been reported to exist in human B lymphocytes in a truncated form capable of binding to broken DNA but lacking the ability to activate the kinase function of DNA-PK. In the present work the Ku70 and Ku86 dimer proteins in T and B lymphocytes from human blood donors were analysed by im munoblotting and were observed apparently to be of full length. Also, nucle ar protein extracted from B and non-B lymphocytes displayed DNA-dependent k inase activity. However, a minor fraction of Ku86 in lymphocytes was observ ed to be truncated with a molecular mass of approx. 70 kDa. (C) 2001 Elsevi er Science B.V. All rights reserved.