Extended -10 elements are recognized by which region of sigma 70?

The correct answer, which identifies that extended -10 elements are recognized by Region 3 of sigma 70, is based on the specific role that each region of the sigma factor plays in promoter recognition during the initiation of transcription in prokaryotic organisms.

Region 3 of sigma 70 is crucial for binding to the extended -10 region, which consists of additional sequences upstream of the classic -10 element (also known as the Pribnow box). This extended region enhances the affinity of RNA polymerase for the promoter, enabling more effective initiation of transcription. The interaction between sigma 70's Region 3 and the extended -10 element contributes to the proper positioning of the RNA polymerase at the transcription start site.

Understanding this molecular interaction is important for grasping the broader mechanics of transcription regulation in bacteria, where sigma factors, like sigma 70, are fundamental for recognizing promoter sequences and helping to initiate the transcription process.