DNA bending by negative regulatory proteins: Gal and Lac repressors

The ability of two negative regulatory proteins, Gal and Lac repressors, to induce DNA bending was tested by the respective cloning of gal and lac operator DNA sequences into a sensitive vector, pBend2. pBend2 can generate a large number of DNA fragments in each of which a cloned operator is present in circularly permuted positions along the length of the DNA. Gel electrophoresis of these DNA fragments individually complexed to a repressor shows that the Gal repressor bends both of the gal operators, OE and OI. Similarly, the Lac repressor induces a bend to a lac operator DNA. In each case, the center of the average bent segment is located at or close to the dyad symmetry axis of the operator sequence. In view of these findings, we discuss how these negative regulatory proteins may function by a more dynamic mechanism than was perceived previously.