Which regions of sigma 70 are associated with binding specific elements?

In transcription initiation in bacteria, sigma factors play a crucial role in promoter recognition by RNA polymerase. Sigma 70, for example, specifically binds to regions of the promoter known as the -10 and -35 elements. These elements are critical for the efficient binding of RNA polymerase to the promoter and the subsequent initiation of transcription.

Region 2 of sigma 70 is particularly important because it contains a helix-turn-helix motif that directly interacts with the -10 element, also known as the Pribnow box. The binding of region 2 to this element is essential for the opening of the DNA double helix and allowing transcription to begin.

Region 4 of sigma 70 is responsible for binding to the -35 element, facilitating the stable attachment of RNA polymerase to the promoter. This interaction is crucial as it helps to position the RNA polymerase correctly for the transcription start.

The other options present incorrect pairings of sigma regions and the promoter elements they bind. Understanding the specific interactions between these regions of sigma 70 and the promoter elements is key to grasping the mechanism of transcription initiation in bacteria.