Bi-column method for purification of transcription factors

A novel bi-column method for purifying transcription factors, using two different columns and two different elution strategies is described. Lac repressor elutes at lower heparin concentrations from a lower affinity lactose operator1 (Op1)-Sepharose column than from a higher affinity column containing the same sequence with a T18:A18 tail (Op1T18). A bi-column method was developed in which lac repressor fusion protein is eluted from the Op1-Sepharose with a low heparin concentration and trapped on a Op1T18-Sepharose column because of its higher affinity for the lac repressor protein. Elution of the latter column with buffer containing a high salt concentration gives significantly purer transcription factor than the conventionally used single column methods and removes residual heparin. Highly pure CAAT enhancer binding protein and the B3 transcription factor are also obtained by using variants of this bi-column method.