Localization of an EGF receptor in purified chromosomes from A431 and lymphoblast cells

Condensed chromosomes from mitotic cells of A431 and lymphoblast GM131 cells were purified by a flow cytometric sorting and collected directly onto nitrocellulose discs. The blots containing purified chromosomes from A431 cells were then hybridized against iodinated protein ligands. Positive autoradiographic signals were obtained from /sup 125/I-epidermal growth factor (EGF), /sup 125/I-calmodulin(CAM)-IgG and /sup 125/I-number528 monoclonal IgG against EGF receptor, but not from /sup 125/I-CAM. Binding of /sup 125/I-EGF to the purified chromosomes on the nitrocellulose was specific and reversible upon the addition of excess unlabeled EGF to the hybridization solutions. Blots containing the purified chromosomes of lymphoblast cells gave positive signals for /sup 125/I-CAM-IgG, while /sup 125/I-CAM signals were not detected. Control experiments showed no detectable contamination from A431 membrane EGF receptor in the purified chromosomal fraction, as demonstrated by the absence of EGF receptor autophosphorylation and the absence of a /sup 125/I-EGF hybridization signal in the supernatant solution of the purified chromosomal preparation.