What is promoter-proximal pausing, and what is its significance in metazoan transcription?

What is promoter-proximal pausing, and what is its significance in metazoan transcription?

• A. RNA Pol II pauses near promoters; release into productive elongation requires regulatory factors like P-TEFb
• B. DNA polymerase pauses near promoters
• C. Pausing occurs only in bacteria
• D. RNA Pol II never pauses

Answer: (A)

Promoter-proximal pausing is a regulated step in transcription where RNA polymerase II begins transcription but stalls shortly after initiation, staying near the promoter in a paused state. This pause is stabilized by factors such as NELF and DSIF, creating a checkpoint that prevents immediate elongation. The transition from pause to productive elongation is tightly controlled: the positive elongation factor P-TEFb (a CDK9/cyclin T complex) phosphorylates the RNA Pol II C-terminal domain as well as NELF and DSIF. This phosphorylation releases NELF, converts DSIF into a positive elongation factor, and allows RNA polymerase II to enter efficient elongation and proper RNA processing. In metazoans, this pausing provides a rapid and flexible means to regulate gene expression in response to developmental and environmental signals, coordinating transcription with RNA capping and processing and enabling quick, synchronized gene activation when needed. The other statements don’t fit because promoter-proximal pausing involves RNA polymerase II, not DNA polymerase; pausing is a feature described in metazoans rather than being exclusive to bacteria; and RNA polymerase II does pause, so saying it never pauses is incorrect.

Promoter-proximal pausing is a regulated step in transcription where RNA polymerase II begins transcription but stalls shortly after initiation, staying near the promoter in a paused state. This pause is stabilized by factors such as NELF and DSIF, creating a checkpoint that prevents immediate elongation. The transition from pause to productive elongation is tightly controlled: the positive elongation factor P-TEFb (a CDK9/cyclin T complex) phosphorylates the RNA Pol II C-terminal domain as well as NELF and DSIF. This phosphorylation releases NELF, converts DSIF into a positive elongation factor, and allows RNA polymerase II to enter efficient elongation and proper RNA processing. In metazoans, this pausing provides a rapid and flexible means to regulate gene expression in response to developmental and environmental signals, coordinating transcription with RNA capping and processing and enabling quick, synchronized gene activation when needed. The other statements don’t fit because promoter-proximal pausing involves RNA polymerase II, not DNA polymerase; pausing is a feature described in metazoans rather than being exclusive to bacteria; and RNA polymerase II does pause, so saying it never pauses is incorrect.