What distinguishes transcription initiation in prokaryotes from eukaryotes?

• A. Prokaryotes require promoter elements like TATA boxes and enhancers; eukaryotes use a sigma factor.
• B. Prokaryotes use RNA polymerase with a sigma factor that binds promoters directly; transcription and translation are coupled; Eukaryotes require multiple transcription factors, promoter elements like TATA, enhancers, chromatin remodeling, and RNA processing.
• C. Prokaryotes have introns; eukaryotes have no introns.
• D. Prokaryotes perform transcription after translation; eukaryotes separate processes in nucleus.

Answer: (B)

At transcription initiation, prokaryotes rely on a single RNA polymerase partnered with a sigma factor that directly recognizes promoter sequences and guides the enzyme to start transcription. This streamlined setup lets transcription begin quickly, and because there is no nucleus, transcription and translation can occur in the same cellular space and even on the same transcript.

In contrast, eukaryotes require a broader assembly of components to kick off transcription. RNA polymerase II works with multiple general transcription factors that bind promoter elements such as a TATA box, as well as other promoter and enhancer elements. Access to DNA is regulated by chromatin remodeling, and once transcription starts, the RNA transcript undergoes processing like capping, splicing, and polyadenylation before it becomes mature mRNA. This added layer of regulation and processing reflects the more complex nuclear environment and the need for tighter control over gene expression.

So the difference boils down to prokaryotes using a sigma factor with a simpler promoter recognition system and coupled transcription–translation, whereas eukaryotes depend on many transcription factors, promoter elements including TATA, chromatin remodeling, and RNA processing to initiate transcription.