Dot blot analysis using crude fusion protein extracts. (A) Bacterial extracts from all eight clones contained fusion proteins capable of binding to anti–β-galactosidase antibodies. (B) Dot blot screening of sera for antibodies to leukemia derived proteins. (Top) Negative reactivity to all eight proteins. (Middle) Positive reactivity to all eight proteins. (Bottom) Positive reactivity to proteins derived from clone no. 5 only. B1, bacterial extract from a clone of blue phage; B2, bacterial extract from a nontransformed E coli.