REQUIREMENT OF PROTEIN CO-FACTOR FOR THE DNA-BINDING FUNCTION OF THE HUMAN SKI PROTO-ONCOGENE PRODUCT

We identified the human c-ski gene product (c-Ski) as a protein with the apparent molecular weight of 100c-ski, by using a c-Ski-specific polyclonal antibody. p100C-Ski was a nuclear protein and p100C-Ski in nuclear extracts of Molt4 cells bound to calf thymus DNA cellulose, but the bacterially synthesized c-Ski did not, suggesting that Ski was associated with another protein(s) and that the Ski complex had DNA-binding activity. This hypothesis was supported by the finding that the bacterially synthesized Ski bounds to DNA cellulose after being mixed with a nuclear extract of Molt4 cells. By use of a series of deletion mutants of Ski synthesized in an in vitro translation system, two portions in Ski were found to be necessary for the DNA binding of the Ski complex: the N-proximal portion containing a cysteinlhistidine-rich domain and the Cterminal portion including a region rich in basic amino acids. © 1990 Oxford University Press.