What is the role of alternative promoters?

• A. They terminate transcription early
• B. They create different transcription start sites, leading to tissue- or condition-specific transcripts
• C. They enhance RNA splicing
• D. They code for different proteins via different reading frames

Answer: (B)

Alternative promoter usage changes where transcription starts, creating transcripts with different 5' ends. This lets the same gene be driven in different ways in different tissues or under different conditions, producing tissue- or condition-specific transcripts and often different protein isoforms or regulatory features.

Transcription termination happens at the end of the gene, not at the promoter, so terminating transcription is not the role of alternative promoters. Splicing is regulated by splice site sequences and splicing factors, not by where transcription begins, so enhancing RNA splicing isn’t the function here. While different transcription start sites can lead to changes in the coding sequence if the new start shifts the reading frame, the core idea of alternative promoters is about initiating transcription at different sites to generate context-specific transcripts, rather than coding for proteins through different reading frames.