DNA-Footprinting using Crude Embryonic Extracts from Xenopus laevis

The interactions of trans-acting factors with cis-acting DNA elements have been a mainstay of molecular biology. With the emergence of new techniques, it is becoming easier to investigate how specific genes are regulated in differentiating cells. In 1978, Galas and Schmitz developed a modified employment of the enzyme deoxyribonuclease I (DNase I) that made it possible to map the DNA-binding site of a putative transcription factor (1 ). With the advent of Maxam and Gilbert sequencing, it also became apparent that chemical nucleases could be used to investigate the nature of protein-DNA interactions (2 ). Although these techniques are applicable to other types of DNA-binding proteins, we will specifically consider transcription factors.