University of Central Florida (UCF) PCB4524 Molecular Biology II Practice Exam 1

In the context of transcription initiation in bacteria, sigma 70 is a subunit of RNA polymerase that plays a critical role in recognizing promoter sequences to initiate transcription. During the melting process, which refers to the unwinding of the DNA double helix to expose the template strand for RNA synthesis, specific regions of sigma 70 are involved in this action.

Region 2.3 of sigma 70 is particularly important because it contains essential amino acids that interact with the DNA. During the melting process, this region is responsible for stabilizing the formation of the transcription bubble, which is the section of unwound DNA where RNA synthesis occurs. In this process, the bases of DNA are flipped out to facilitate their interaction with RNA polymerase and to allow for the appropriate base pairing with ribonucleotides.

The distinction of region 2.3 is significant because it precisely mediates the DNA melting and leads to a stable open complex formation necessary for transcription to commence. Thus, its role in flipping out the bases during the melting process highlights its crucial function in transcription initiation.

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